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).

5 files changed, 18 insertions, 9 deletions

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>