add /WX mscv compiler option for only mscv compiler

clang on windows support both gcc and mscv style options. Clang.exe on windows
defaults to gcc style, which will result in /WX unknown compiler command.
This will set /WX if and only if the compiler is MSVC and greater than version 1900

cmake/utils.cmake

@@ -28,13 +28,15 @@ endfunction()
 
 # Turn on warnings on the given target
 function(spdlog_enable_warnings target_name)
+	set(MSVC_OPTIONS "/W3")
+	if(MSVC_VERSION GREATER  1900)  #Allow non fatal security wanrnings for msvc 2015
+		set(MSVC_OPTIONS "${MSVC_OPTIONS} /WX")
+	endif()
     target_compile_options(${target_name} PRIVATE
         $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:GNU>>:
             -Wall -Wextra -Wconversion -pedantic -Wfatal-errors>
-        $<$<CXX_COMPILER_ID:MSVC>:/W3>)
-		if(MSVC_VERSION GREATER  1900)  #Allow non fatal security wanrnings for msvc 2015
-			target_compile_options(${target_name} PRIVATE /WX)
-		endif()
+        $<$<CXX_COMPILER_ID:MSVC>:${MSVC_OPTIONS}>)
+
 endfunction()