Enable cross compilation of Windows targets on Linux (#839)

This PR makes it *possible* to do a Windows build on Linux via `clang-cl`. 

It doesn't actually change any build process. No policy change, just mechanics and some code fixes to clear clang compilation.

The code fixes are mainly related to #include file name casing, to match the on-disk casing of the SDK files (via xwin).

18 files changed, 57 insertions, 27 deletions

diff --git a/src/transports/winsock/xmake.lua b/src/transports/winsock/xmake.lua
index c14283546..cdba75885 100644
--- a/src/transports/winsock/xmake.lua
+++ b/src/transports/winsock/xmake.lua
@@ -5,7 +5,7 @@ target("winsock")
     set_group("transports")
     add_headerfiles("**.h")
     add_files("**.cpp")
-    add_links("Ws2_32")
+    add_links("ws2_32")
     add_includedirs(".")
     set_symbols("debug")
     add_deps("zenbase", "transport-sdk")
diff --git a/src/zen/cmds/service_cmd.cpp b/src/zen/cmds/service_cmd.cpp
index a781dc340..3347f1afe 100644
--- a/src/zen/cmds/service_cmd.cpp
+++ b/src/zen/cmds/service_cmd.cpp
@@ -12,8 +12,8 @@
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
 #	include <shellapi.h>
-#	include <Shlwapi.h>
-#	pragma comment(lib, "Shlwapi.lib")
+#	include <shlwapi.h>
+#	pragma comment(lib, "shlwapi.lib")
 #endif
 
 #if ZEN_PLATFORM_LINUX || ZEN_PLATFORM_MAC
diff --git a/src/zen/xmake.lua b/src/zen/xmake.lua
index 4c134404a..df249ade4 100644
--- a/src/zen/xmake.lua
+++ b/src/zen/xmake.lua
@@ -14,8 +14,10 @@ target("zen")
 
     if is_plat("windows") then
         add_files("zen.rc")
-        add_ldflags("/subsystem:console,5.02")
-        add_ldflags("/LTCG")
+        add_ldflags("/subsystem:console,5.02", {force = true})
+        if not (get_config("toolchain") or ""):find("clang") then
+            add_ldflags("/LTCG")
+        end
     end
 
     if is_plat("macosx") then
diff --git a/src/zen/zen.rc b/src/zen/zen.rc
index 0617681a7..3adf25b72 100644
--- a/src/zen/zen.rc
+++ b/src/zen/zen.rc
@@ -7,7 +7,7 @@
 LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
 #pragma code_page(1252)
 
-101               ICON                    "..\\zen.ico"
+101               ICON                    "../zen.ico"
 
 VS_VERSION_INFO VERSIONINFO
 FILEVERSION    ZEN_CFG_VERSION_MAJOR,ZEN_CFG_VERSION_MINOR,ZEN_CFG_VERSION_ALTER,0
diff --git a/src/zenbase/include/zenbase/zenbase.h b/src/zenbase/include/zenbase/zenbase.h
index 2aec1f314..1d5051c5b 100644
--- a/src/zenbase/include/zenbase/zenbase.h
+++ b/src/zenbase/include/zenbase/zenbase.h
@@ -211,7 +211,24 @@ char (&ZenArrayCountHelper(const T (&)[N]))[N + 1];
 #	define ZEN_EXE_SUFFIX_LITERAL ""
 #endif
 
-#define ZEN_UNUSED(...) ((void)__VA_ARGS__)
+#if ZEN_COMPILER_CLANG
+// Clang warns about the comma operator in ((void)a, b) with -Wunused-value.
+// Use a fold expression via a helper to suppress each argument individually.
+namespace zen::detail {
+inline void
+unused_impl()
+{
+}
+template<typename... T>
+inline void
+unused_impl(T&&...)
+{
+}
+}  // namespace zen::detail
+#	define ZEN_UNUSED(...) ::zen::detail::unused_impl(__VA_ARGS__)
+#else
+#	define ZEN_UNUSED(...) ((void)__VA_ARGS__)
+#endif
 
 //////////////////////////////////////////////////////////////////////////
 
diff --git a/src/zencore-test/targetver.h b/src/zencore-test/targetver.h
index d432d6993..4805141de 100644
--- a/src/zencore-test/targetver.h
+++ b/src/zencore-test/targetver.h
@@ -7,4 +7,4 @@
 // If you wish to build your application for a previous Windows platform, include WinSDKVer.h and
 // set the _WIN32_WINNT macro to the platform you wish to support before including SDKDDKVer.h.
 
-#include <SDKDDKVer.h>
+#include <sdkddkver.h>
diff --git a/src/zencore/callstack.cpp b/src/zencore/callstack.cpp
index ee0b0625a..a16bb3f13 100644
--- a/src/zencore/callstack.cpp
+++ b/src/zencore/callstack.cpp
@@ -6,7 +6,7 @@
 
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
-#	include <Dbghelp.h>
+#	include <DbgHelp.h>
 #endif
 
 #if ZEN_PLATFORM_LINUX || ZEN_PLATFORM_MAC
diff --git a/src/zencore/filesystem.cpp b/src/zencore/filesystem.cpp
index e557b376c..0d361801f 100644
--- a/src/zencore/filesystem.cpp
+++ b/src/zencore/filesystem.cpp
@@ -17,7 +17,7 @@
 
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
-#	include <ShlObj.h>
+#	include <shlobj.h>
 #	pragma comment(lib, "shell32.lib")
 #	pragma comment(lib, "ole32.lib")
 #endif
diff --git a/src/zencore/include/zencore/string.h b/src/zencore/include/zencore/string.h
index 7b46f0e38..60293a313 100644
--- a/src/zencore/include/zencore/string.h
+++ b/src/zencore/include/zencore/string.h
@@ -333,7 +333,8 @@ public:
 
 #if defined(__clang__) && !defined(__APPLE__) && !defined(_MSC_VER)
 	/* UE Toolchain Clang has different types for int64_t and long long so an override is
-	needed here. Without it, Clang can't disambiguate integer overloads */
+	needed here. Without it, Clang can't disambiguate integer overloads.
+	On MSVC ABI (including clang-cl), int64_t is long long so no separate overload is needed. */
 	inline StringBuilderImpl& operator<<(long long n)
 	{
 		IntNum Str(n);
diff --git a/src/zencore/memtrack/callstacktrace.cpp b/src/zencore/memtrack/callstacktrace.cpp
index 013c51535..ccbea1282 100644
--- a/src/zencore/memtrack/callstacktrace.cpp
+++ b/src/zencore/memtrack/callstacktrace.cpp
@@ -193,8 +193,12 @@ private:
 	std::atomic_uint32_t	 CallstackIdCounter{1};	 // 0 is reserved for "unknown callstack"
 };
 
+}  // namespace zen
+
 #	if UE_CALLSTACK_TRACE_USE_UNWIND_TABLES
 
+namespace zen {
+
 /*
  * Windows' x64 binaries contain a ".pdata" section that describes the location
  * and size of its functions and details on how to unwind them. The unwind
@@ -908,10 +912,12 @@ FBacktracer::GetBacktraceId(void* AddressOfReturnAddress)
 	// queue (i.e. the processing thread has caught up processing).
 	return CallstackTracer.AddCallstack(BacktraceEntry);
 }
-}
+}  // namespace zen
 
 #	else  // UE_CALLSTACK_TRACE_USE_UNWIND_TABLES
 
+namespace zen {
+
 ////////////////////////////////////////////////////////////////////////////////
 class FBacktracer
 {
@@ -921,8 +927,8 @@ public:
 	static FBacktracer* Get();
 	inline uint32_t		GetBacktraceId(void* AddressOfReturnAddress);
 	uint32_t			GetBacktraceId(uint64_t ReturnAddress);
-	void				AddModule(uintptr_t Base, const char16_t* Name) {}
-	void				RemoveModule(uintptr_t Base) {}
+	void				AddModule(uintptr_t /*Base*/, const char16_t* /*Name*/) {}
+	void				RemoveModule(uintptr_t /*Base*/) {}
 
 private:
 	static FBacktracer* Instance;
@@ -963,6 +969,7 @@ FBacktracer::GetBacktraceId(void* AddressOfReturnAddress)
 uint32_t
 FBacktracer::GetBacktraceId(uint64_t ReturnAddress)
 {
+	ZEN_UNUSED(ReturnAddress);
 #		if !UE_BUILD_SHIPPING
 	uint64_t StackFrames[256];
 	int32_t	 NumStackFrames = FPlatformStackWalk::CaptureStackBackTrace(StackFrames, UE_ARRAY_COUNT(StackFrames));
@@ -1006,7 +1013,8 @@ FBacktracer::GetBacktraceId(uint64_t ReturnAddress)
 
 	return 0;
 }
-}
+
+}  // namespace zen
 
 #	endif	// UE_CALLSTACK_TRACE_USE_UNWIND_TABLES
 
diff --git a/src/zencore/process.cpp b/src/zencore/process.cpp
index 852678ffe..080607f13 100644
--- a/src/zencore/process.cpp
+++ b/src/zencore/process.cpp
@@ -21,8 +21,8 @@ ZEN_THIRD_PARTY_INCLUDES_START
 
 #	include <Psapi.h>
 #	include <shellapi.h>
-#	include <Shlobj.h>
-#	include <TlHelp32.h>
+#	include <shlobj.h>
+#	include <tlhelp32.h>
 #else
 #	include <fcntl.h>
 #	include <pthread.h>
diff --git a/src/zenhorde/hordetransportaes.cpp b/src/zenhorde/hordetransportaes.cpp
index 986dd3705..505b6bde7 100644
--- a/src/zenhorde/hordetransportaes.cpp
+++ b/src/zenhorde/hordetransportaes.cpp
@@ -12,7 +12,7 @@
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
 #	include <bcrypt.h>
-#	pragma comment(lib, "Bcrypt.lib")
+#	pragma comment(lib, "bcrypt.lib")
 #else
 ZEN_THIRD_PARTY_INCLUDES_START
 #	include <openssl/evp.h>
diff --git a/src/zenhttp/servers/httpplugin.cpp b/src/zenhttp/servers/httpplugin.cpp
index a1bb719c8..31b0315d4 100644
--- a/src/zenhttp/servers/httpplugin.cpp
+++ b/src/zenhttp/servers/httpplugin.cpp
@@ -147,7 +147,7 @@ public:
 	HttpPluginServerRequest& operator=(const HttpPluginServerRequest&) = delete;
 
 	// As this is plugin transport connection used for specialized connections we assume it is not a machine local connection
-	bool					 IsLocalMachineRequest() const override { return false; }
+	virtual bool			 IsLocalMachineRequest() const override { return false; }
 	virtual std::string_view GetAuthorizationHeader() const override;
 	virtual Oid				 ParseSessionId() const override;
 	virtual uint32_t		 ParseRequestId() const override;
diff --git a/src/zenhttp/servers/httpsys.cpp b/src/zenhttp/servers/httpsys.cpp
index 4d6a53696..f8fb1c9be 100644
--- a/src/zenhttp/servers/httpsys.cpp
+++ b/src/zenhttp/servers/httpsys.cpp
@@ -1173,7 +1173,7 @@ HttpSysServer::RegisterHttpUrls(int BasePort)
 	{
 		Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, WildcardUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
 
-		if ((Result == ERROR_SHARING_VIOLATION))
+		if (Result == ERROR_SHARING_VIOLATION)
 		{
 			ZEN_INFO("Desired port {} is in use (HttpAddUrlToUrlGroup returned: {}), retrying",
 					 EffectivePort,
diff --git a/src/zenserver/storage/vfs/vfsservice.cpp b/src/zenserver/storage/vfs/vfsservice.cpp
index 863ec348a..f418c4131 100644
--- a/src/zenserver/storage/vfs/vfsservice.cpp
+++ b/src/zenserver/storage/vfs/vfsservice.cpp
@@ -62,7 +62,7 @@ GetContentAsCbObject(HttpServerRequest& HttpReq, CbObject& Cb)
 // echo {"method": "mount", "params": {"path": "d:\\VFS_ROOT"}} | curl.exe http://localhost:8558/vfs --data-binary @-
 // echo {"method": "unmount"} | curl.exe http://localhost:8558/vfs --data-binary @-
 
-VfsService::VfsService(HttpStatusService& StatusService, VfsServiceImpl* ServiceImpl) : m_StatusService(StatusService), m_Impl(ServiceImpl)
+VfsService::VfsService(HttpStatusService& StatusService, VfsServiceImpl* ServiceImpl) : m_Impl(ServiceImpl), m_StatusService(StatusService)
 {
 	m_Router.RegisterRoute(
 		"info",
diff --git a/src/zenserver/targetver.h b/src/zenserver/targetver.h
index d432d6993..4805141de 100644
--- a/src/zenserver/targetver.h
+++ b/src/zenserver/targetver.h
@@ -7,4 +7,4 @@
 // If you wish to build your application for a previous Windows platform, include WinSDKVer.h and
 // set the _WIN32_WINNT macro to the platform you wish to support before including SDKDDKVer.h.
 
-#include <SDKDDKVer.h>
+#include <sdkddkver.h>
diff --git a/src/zenserver/xmake.lua b/src/zenserver/xmake.lua
index 52889fff5..6b29dadfb 100644
--- a/src/zenserver/xmake.lua
+++ b/src/zenserver/xmake.lua
@@ -60,13 +60,15 @@ target("zenserver")
     end
 
     if is_plat("windows") then
-        add_ldflags("/subsystem:console,5.02")
-        add_ldflags("/MANIFEST:EMBED")
-        add_ldflags("/LTCG")
+        add_ldflags("/subsystem:console,5.02", {force = true})
+        add_ldflags("/MANIFEST:EMBED", {force = true})
+        if not (get_config("toolchain") or ""):find("clang") then
+            add_ldflags("/LTCG")
+        end
         add_files("zenserver.rc")
         add_cxxflags("/bigobj")
         add_links("delayimp", "projectedfslib")
-        add_ldflags("/delayload:ProjectedFSLib.dll")
+        add_ldflags("/delayload:ProjectedFSLib.dll", {force = true})
     else
         remove_files("windows/**")
     end
diff --git a/src/zenserver/zenserver.rc b/src/zenserver/zenserver.rc
index f353bd9cc..abe1acf71 100644
--- a/src/zenserver/zenserver.rc
+++ b/src/zenserver/zenserver.rc
@@ -28,7 +28,7 @@ LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
 
 // Icon with lowest ID value placed first to ensure application icon
 // remains consistent on all systems.
-IDI_ICON1               ICON                    "..\\zen.ico"
+IDI_ICON1               ICON                    "../zen.ico"
 
 #endif    // English (United States) resources
 /////////////////////////////////////////////////////////////////////////////