Fix SDL_PRIs64 to use standard PRId64

PRIs64 doesn't exist in C standards.

(cherry picked from commit 8a2cac7)

Author: zturtleman

include/SDL_stdinc.h

@@ -268,8 +268,8 @@ typedef uint64_t Uint64;
 #ifndef SDL_PRIs64
 #if defined(__WIN32__) || defined(__GDK__)
 #define SDL_PRIs64 "I64d"
-#elif defined(PRIs64)
-#define SDL_PRIs64 PRIs64
+#elif defined(PRId64)
+#define SDL_PRIs64 PRId64
 #elif defined(__LP64__) && !defined(__APPLE__) && !defined(__EMSCRIPTEN__)
 #define SDL_PRIs64 "ld"
 #else