Try to fix MinGW ci

.github/workflows/msys2-build.yml

@@ -92,7 +92,7 @@ jobs:
 
     # Setup compilation mode and install project dependencies
     - name: Configure xmake and install dependencies
-      run: xmake config --arch=${{ matrix.arch }} --mode=${{ matrix.mode }} --ccache=n --ffmpeg=y --shadernodes=y --tests=y --unitybuild=y --yes --verbose --diagnosis
+      run: xmake config --arch=${{ matrix.arch }} --mode=${{ matrix.mode }} --ccache=n --ffmpeg=y --shadernodes=y --tests=y --unitybuild=y --yes --verbose --diagnosis --policies=package.include_external_headers:n
 
     # Build the engine
     - name: Build Nazara

xmake.lua

@@ -205,10 +205,6 @@ if is_plat("windows") then
 elseif is_plat("mingw") then
 	add_cxflags("-Og", "-Wa,-mbig-obj")
 	add_ldflags("-Wa,-mbig-obj")
-
-	if is_subhost("msys", "cygwin") then
-		add_rules("msys2.isystem.fix")
-	end
 end
 
 for name, module in pairs(modules) do

xmake/rules/msys2_isystem_fix.lua

@@ -1,14 +0,0 @@
-rule("msys2.isystem.fix")
-	on_load(function (target)
-		import("core.project.project")
-
-		local external = project.policy("package.include_external_headers")
-		if external == nil then
-			external = target:policy("package.include_external_headers")
-		end
-
-		-- disable -isystem for packages as it seems broken on msys2 (see https://github.com/msys2/MINGW-packages/issues/10761)
-		if external == nil then
-			target:set("policy", "package.include_external_headers", false)
-		end	
-	end)