SDL_atomic.h rename fixes

Adding following macro to SDL_oldnames.h:
SDL_atomic_t SDL_atomic_t_renamed_SDL_AtomicInt

include/SDL3/SDL_oldnames.h

@@ -551,6 +551,7 @@
 #define SDL_AtomicLock SDL_AtomicLock_renamed_SDL_LockSpinlock
 #define SDL_AtomicTryLock SDL_AtomicTryLock_renamed_SDL_TryLockSpinlock
 #define SDL_AtomicUnlock SDL_AtomicUnlock_renamed_SDL_UnlockSpinlock
+#define SDL_atomic_t SDL_atomic_t_renamed_SDL_AtomicInt
 
 /* ##SDL_audio.h */
 #define AUDIO_F32 AUDIO_F32_renamed_SDL_AUDIO_F32LE