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

test/testwm.c

@@ -10,14 +10,14 @@
   freely.
 */
 
-#ifdef __EMSCRIPTEN__
-#include <emscripten/emscripten.h>
-#endif
-
 #include <SDL3/SDL_test_common.h>
 #include <SDL3/SDL_test_font.h>
 #include <SDL3/SDL_main.h>
 
+#ifdef SDL_PLATFORM_EMSCRIPTEN
+#include <emscripten/emscripten.h>
+#endif
+
 static SDLTest_CommonState *state;
 static int done;
 
@@ -248,7 +248,7 @@ static void loop(void)
             SDL_RenderPresent(renderer);
         }
     }
-#ifdef __EMSCRIPTEN__
+#ifdef SDL_PLATFORM_EMSCRIPTEN
     if (done) {
         emscripten_cancel_main_loop();
     }
@@ -281,7 +281,7 @@ int main(int argc, char *argv[])
 
     /* Main render loop */
     done = 0;
-#ifdef __EMSCRIPTEN__
+#ifdef SDL_PLATFORM_EMSCRIPTEN
     emscripten_set_main_loop(loop, 0, 1);
 #else
     while (!done) {