SDL_endian.h: don't add _m_prefetch hack for clang-cl if available as a builtin

Fixes: https://github.com/libsdl-org/SDL/issues/13952 .

(backport from SDL3 commit 81f2f4484392883e6ecbb2f4b04c99c0174d6bff)

include/SDL_endian.h

@@ -33,7 +33,7 @@
 #if defined(_MSC_VER) && (_MSC_VER >= 1400)
 /* As of Clang 11, '_m_prefetchw' is conflicting with the winnt.h's version,
    so we define the needed '_m_prefetch' here as a pseudo-header, until the issue is fixed. */
-#ifdef __clang__
+#if defined(__clang__) && !SDL_HAS_BUILTIN(_m_prefetch)
 #ifndef __PRFCHWINTRIN_H
 #define __PRFCHWINTRIN_H
 static __inline__ void __attribute__((__always_inline__, __nodebug__))