revive UE toolchain build (#343)

* add comment about 7z usage in xmake bundle
* add ue-libcxx lib/headers and licence + tps
* update get_ue_toolchain.sh to use embedded libc++ and decouple from p4
* clearer output when falling back to zip from 7z
* update ci scripts to use ue toolchain on linux
* updated linux build README.md
* changelog

1 files changed, 2 insertions, 1 deletions

diff --git a/xmake.lua b/xmake.lua
index 930ef65c1..ac01f4694 100644
--- a/xmake.lua
+++ b/xmake.lua
@@ -30,7 +30,8 @@ else
 end
 
 if is_plat("windows") then
-    add_requires("7z") -- for bundling
+    -- for bundling, linux tries to compile from source which fails with UE toolchain, fallback is regular zip
+    add_requires("7z")
 end
 
 if not is_arch("arm64") then