Buildsystem: Minor PCH building changes

* *PCH.cpp are now only compiled with MSVC, other compilers use custom helper commands to generate the precompiled header
* Don't call the linker for pch helpertargets

(cherry picked from commit 137f5e78877ef1b81f4dca68dd43268e325aeeed)

cmake/macros/FindPCHSupport.cmake

@@ -85,7 +85,7 @@ FUNCTION(GENERATE_CXX_PCH_COMMAND TARGET_NAME_LIST INCLUDE_FLAGS IN PCH_SRC OUT)
   ADD_CUSTOM_COMMAND(
     OUTPUT ${OUT}
     COMMAND ${CMAKE_CXX_COMPILER}
-    ARGS ${DEFINITION_FLAGS} ${COMPILE_FLAGS} ${INCLUDE_FLAGS} -x c++-header ${IN} -o ${OUT}
+    ARGS ${DEFINITION_FLAGS} ${COMPILE_FLAGS} ${INCLUDE_FLAGS} -x c++-header -c ${IN} -o ${OUT}
     DEPENDS ${IN} ${PCH_SRC_N}_dephelp
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
   )