Correct cmake for windows

CMakeLists.txt

@@ -136,8 +136,8 @@ include(ftl_paths)
 if (WIN32) # TODO(nick) Should do based upon compiler (VS)
 	add_definitions(-DWIN32)
 	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
-	set(CMAKE_CXX_FLAGS_DEBUG "-DFTL_DEBUG -Wall")
-	set(CMAKE_CXX_FLAGS_RELEASE "/O2")
+	set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /DFTL_DEBUG /Wall")
+	set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /O2")
 	set(OS_LIBS "")
 else()
 	add_definitions(-DUNIX)