Specify the current runtime version to target if the compiler supports this

flag.  This means that the .m files in the runtime will take advantage of
features of this runtime when compiled with a recent clang.

CMakeLists.txt

@@ -120,6 +120,9 @@ endif ()
 
 if (${CMAKE_C_COMPILER_ID} MATCHES Clang*)
 	set(CMAKE_OBJC_FLAGS "${CMAKE_OBJC_FLAGS} -Wno-deprecated-objc-isa-usage -Wno-objc-root-class")
+	if (${CMAKE_C_COMPILER_VERSION} VERSION_GREATER 3.1)
+		set(CMAKE_OBJC_FLAGS "${CMAKE_OBJC_FLAGS} -fobjc-runtime=gnustep-1.7")
+	endif ()
 	if (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "i686")
 		set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=i586")
 	endif ()