Improve check for conflicting config_kernel.h

Author: martin-frbg

cmake/arch.cmake

@@ -83,8 +83,7 @@ if (DYNAMIC_ARCH)
     endif ()
   endif ()
 
-  CHECK_INCLUDE_FILE ("${PROJECT_SOURCE_DIR}/config_kernel.h" TRAP)
-  if (TRAP)
+  if (EXISTS ${PROJECT_SOURCE_DIR}/config_kernel.h)
 	  message (FATAL_ERROR "Your build directory contains a file config_kernel.h, probably from a previous compilation with make. This will conflict with the cmake compilation and cause strange compiler errors - please remove the file before trying again")
   endif ()