Check whether -Wno-unused-but-set-variable is supported before using

it. It seems to only be available on recent (>=4.6) versions of gcc.

Author: AMDmi3

src/CMakeLists.txt

@@ -209,6 +209,8 @@ endif(BUILD_SERVER)
 # Set some optimizations and tweaks
 #
 
+include(CheckCCompilerFlag)
+
 if(MSVC)
 	# Visual Studio
 
@@ -236,7 +238,10 @@ else()
 	endif()
 
 	if(NOT APPLE)
-		set(WARNING_FLAGS "${WARNING_FLAGS} -Wno-unused-but-set-variable")
+		check_c_compiler_flag("-Wno-unused-but-set-variable" HAS_UNUSED_BUT_SET_VARIABLE_WARNING)
+		if(HAS_UNUSED_BUT_SET_VARIABLE_WARNING)
+			set(WARNING_FLAGS "${WARNING_FLAGS} -Wno-unused-but-set-variable")
+		endif(HAS_UNUSED_BUT_SET_VARIABLE_WARNING)
 	endif()
 
 	if(APPLE)