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

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4