[embedded] Concurrency/CMakeLists.txt: Use -isystem instead of -I for SDK search paths

Author: kubamracek

stdlib/public/Concurrency/CMakeLists.txt

@@ -287,7 +287,7 @@ if(SWIFT_SHOULD_BUILD_EMBEDDED_STDLIB AND SWIFT_SHOULD_BUILD_EMBEDDED_CONCURRENC
       if(NOT "${mod}" MATCHES "-apple-" OR "${mod}" MATCHES "-none-macho")
         # Host is macOS with a macOS SDK. To be able to build the C++ Concurrency runtime for non-Darwin targets using the macOS SDK,
         # we need to pass some extra flags and search paths.
-        set(extra_c_compile_flags -stdlib=libc++ -I${SWIFT_SDK_OSX_PATH}/usr/include/c++/v1 -I${SWIFT_SDK_OSX_PATH}/usr/include -D__APPLE__)
+        set(extra_c_compile_flags -stdlib=libc++ -isystem${SWIFT_SDK_OSX_PATH}/usr/include/c++/v1 -isystem${SWIFT_SDK_OSX_PATH}/usr/include -D__APPLE__)
       endif()
     endif()