create MSVC_OPTIONS list only if compiler is msvc

cmake/utils.cmake

@@ -28,10 +28,13 @@ endfunction()
 
 # Turn on warnings on the given target
 function(spdlog_enable_warnings target_name)
-	list(APPEND MSVC_OPTIONS "/W3")
-	if(MSVC_VERSION GREATER  1900)  #Allow non fatal security wanrnings for msvc 2015
-		list(APPEND MSVC_OPTIONS "/WX")
+	if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+		list(APPEND MSVC_OPTIONS "/W3")
+		if(MSVC_VERSION GREATER  1900)  #Allow non fatal security wanrnings for msvc 2015
+			list(APPEND MSVC_OPTIONS "/WX")
+		endif()
 	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>