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

test/testrendertarget.c

@@ -11,16 +11,16 @@
 */
 /* Simple program:  Move N sprites around on the screen as fast as possible */
 
-#include <stdlib.h>
-
-#ifdef __EMSCRIPTEN__
-#include <emscripten/emscripten.h>
-#endif
-
 #include <SDL3/SDL_test_common.h>
 #include <SDL3/SDL_main.h>
 #include "testutils.h"
 
+#ifdef SDL_PLATFORM_EMSCRIPTEN
+#include <emscripten/emscripten.h>
+#endif
+
+#include <stdlib.h>
+
 static SDLTest_CommonState *state;
 
 typedef struct
@@ -199,7 +199,7 @@ static void loop(void)
             }
         }
     }
-#ifdef __EMSCRIPTEN__
+#ifdef SDL_PLATFORM_EMSCRIPTEN
     if (done) {
         emscripten_cancel_main_loop();
     }
@@ -269,7 +269,7 @@ int main(int argc, char *argv[])
     then = SDL_GetTicks();
     done = 0;
 
-#ifdef __EMSCRIPTEN__
+#ifdef SDL_PLATFORM_EMSCRIPTEN
     emscripten_set_main_loop(loop, 0, 1);
 #else
     while (!done) {