[core] code size: disable XXH64(), XXH3()

only XXH32() is used by ls-hpack, so disable XXH64() and XXH3()
to reduce code size.  (This maybe be changed in the future if
XXH64() or XXH3() are utilitized for their performance)

src/algo_xxhash.h

@@ -1,6 +1,7 @@
 /*(lighttpd customization)*/
-#define XXH_NO_INLINE_HINTS 1
+/*#define XXH_NO_INLINE_HINTS 1*/
 /*#define XXH_REROLL 1*/
+#define XXH_NO_LONG_LONG
 
 /*
  * xxHash - Extremely Fast Hash algorithm