atomic: Switch to SDL_HAS_BUILTIN to detect __atomic_load_n

src/atomic/SDL_atomic.c

@@ -34,19 +34,15 @@
 #endif
 
 // The __atomic_load_n() intrinsic showed up in different times for different compilers.
-#ifdef __clang__
-#if __has_builtin(__atomic_load_n) || defined(HAVE_GCC_ATOMICS)
+#if defined(__GNUC__) && (__GNUC__ >= 5)
+#define HAVE_ATOMIC_LOAD_N 1
+#elif SDL_HAS_BUILTIN(__atomic_load_n) || (defined(__clang__) && defined(HAVE_GCC_ATOMICS))
 /* !!! FIXME: this advertises as available in the NDK but uses an external symbol we don't have.
    It might be in a later NDK or we might need an extra library? --ryan. */
 #ifndef SDL_PLATFORM_ANDROID
 #define HAVE_ATOMIC_LOAD_N 1
 #endif
 #endif
-#elif defined(__GNUC__)
-#if (__GNUC__ >= 5)
-#define HAVE_ATOMIC_LOAD_N 1
-#endif
-#endif
 
 /*
   If any of the operations are not provided then we must emulate some