Fixed bug 2238 - Enable GCC atomics for clang

Marcus von Appen

clang provides support for optimized atomics.
The attached patch enables the cmake build system to take clang into account on checking for atomics.

CMakeLists.txt

@@ -266,7 +266,7 @@ endif(ASSERTIONS STREQUAL "auto")
 set(HAVE_ASSERTIONS ${ASSERTIONS})
 
 # Compiler option evaluation
-if(USE_GCC)
+if(USE_GCC OR USE_CLANG)
   if(DEPENDENCY_TRACKING)
     check_c_source_compiles("
         #if !defined(__GNUC__) || __GNUC__ < 3
@@ -314,7 +314,7 @@ if(USE_GCC)
       set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-multichar")
     endif(HAIKU)
   endif(HAVE_GCC_WALL)
-endif(USE_GCC)
+endif(USE_GCC OR USE_CLANG)
 
 if(ASSEMBLY)
   if(USE_GCC OR USE_CLANG)