As reported in oss-fuzz issue 22388, the contrib/hpack code doesn't
build anymore for now. Thanks to previous patch we can now just define
HPACK_STANDALONE in the few files which include hpack-tbl.h and we can
declare a dummy pool to hold the DHT size. This is enough to make the
code work again outside of the haproxy process. It was successfully
tested using:
$ echo 82 84 87 90 | ./decode
318adf4364