Define SDL_PLATFORM_* macros instead of underscored ones (#8875)

test/testime.c

@@ -27,9 +27,9 @@
 #endif
 
 #ifdef HAVE_SDL_TTF
-#ifdef __MACOS__
+#ifdef SDL_PLATFORM_MACOS
 #define DEFAULT_FONT "/System/Library/Fonts/华文细黑.ttf"
-#elif defined(__WIN32__)
+#elif defined(SDL_PLATFORM_WIN32)
 /* Some japanese font present on at least Windows 8.1. */
 #define DEFAULT_FONT "C:\\Windows\\Fonts\\yugothic.ttf"
 #else