Use the printf vararg verification macros when compiling with clang

include/SDL3/SDL_stdinc.h

@@ -554,7 +554,7 @@ SDL_COMPILE_TIME_ASSERT(longlong_size64, sizeof(long long) == 8); /* using I64 f
 #define SDL_PRINTF_FORMAT_STRING
 #define SDL_SCANF_FORMAT_STRING
 #endif
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #define SDL_PRINTF_VARARG_FUNC( fmtargnumber ) __attribute__ (( format( __printf__, fmtargnumber, fmtargnumber+1 )))
 #define SDL_PRINTF_VARARG_FUNCV( fmtargnumber ) __attribute__(( format( __printf__, fmtargnumber, 0 )))
 #define SDL_SCANF_VARARG_FUNC( fmtargnumber ) __attribute__ (( format( __scanf__, fmtargnumber, fmtargnumber+1 )))