Fix -Wundef warnings due to use of unguarded __ANDROID__

src/SDL.c

@@ -620,7 +620,7 @@ SDL_GetPlatform(void)
 SDL_bool
 SDL_IsTablet(void)
 {
-#if __ANDROID__
+#if defined(__ANDROID__)
     extern SDL_bool SDL_IsAndroidTablet(void);
     return SDL_IsAndroidTablet();
 #elif __IOS__

src/video/SDL_video.c

@@ -192,7 +192,7 @@ typedef struct
 
 static Uint32 SDL_DefaultGraphicsBackends(SDL_VideoDevice *_this)
 {
-#if (SDL_VIDEO_OPENGL && __MACOS__) || (__IOS__ && !TARGET_OS_MACCATALYST) || __ANDROID__
+#if (SDL_VIDEO_OPENGL && __MACOS__) || (__IOS__ && !TARGET_OS_MACCATALYST) || defined(__ANDROID__)
     if (_this->GL_CreateContext != NULL) {
         return SDL_WINDOW_OPENGL;
     }