Merge topic 'dev/add-isystem-for-clang'

4d668f3 Clang: Add -isystem flag support everywhere

Modules/Compiler/Clang.cmake

@@ -23,4 +23,5 @@ include(Compiler/GNU)
 macro(__compiler_clang lang)
   __compiler_gnu(${lang})
   set(CMAKE_${lang}_COMPILE_OPTIONS_PIE "-fPIE")
+  set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-isystem ")
 endmacro()