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

src/misc/ios/SDL_sysurl.m

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if defined(__IOS__) || defined(__TVOS__)
+#if defined(SDL_PLATFORM_IOS) || defined(SDL_PLATFORM_TVOS)
 
 #include "../SDL_sysurl.h"
 
@@ -40,4 +40,4 @@ int SDL_SYS_OpenURL(const char *url)
     }
 }
 
-#endif /* __IOS__ || __TVOS__ */
+#endif /* SDL_PLATFORM_IOS || SDL_PLATFORM_TVOS */

src/misc/macos/SDL_sysurl.m

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if defined(__MACOS__)
+#if defined(SDL_PLATFORM_MACOS)
 
 #include "../SDL_sysurl.h"
 
@@ -36,4 +36,4 @@ int SDL_SYS_OpenURL(const char *url)
     }
 }
 
-#endif /* __MACOS__ */
+#endif /* SDL_PLATFORM_MACOS */

src/misc/windows/SDL_sysurl.c

@@ -25,7 +25,7 @@
 
 #include <shellapi.h>
 
-#if defined(__XBOXONE__) || defined(__XBOXSERIES__)
+#if defined(SDL_PLATFORM_XBOXONE) || defined(SDL_PLATFORM_XBOXSERIES)
 int SDL_SYS_OpenURL(const char *url)
 {
     /* Not supported */