Use XXH64 on 64-bit systems.

I'm not able to reproduce any real performance difference, but I know
there are some games which do more hashing and it may help there.

GPU/GLES/TextureCache.cpp

@@ -921,7 +921,7 @@ void TextureCache::UpdateCurrentClut() {
 	// If not, we're going to hash random data, which hopefully doesn't cause a performance issue.
 	const u32 clutExtendedBytes = clutTotalBytes_ + clutBaseBytes;
 
-	clutHash_ = DoReliableHash((const char *)clutBufRaw_, clutExtendedBytes, 0xC0108888);
+	clutHash_ = DoReliableHash32((const char *)clutBufRaw_, clutExtendedBytes, 0xC0108888);
 
 	// Avoid a copy when we don't need to convert colors.
 	if (UseBGRA8888() || clutFormat != GE_CMODE_32BIT_ABGR8888) {