zstd: hack include order to ensure that our zstd.h is found
If the regular Python CFLAGS include directories that already have the
zstd headers available, a different and possible incompatible version
can be picked up otherwise. Sadly, it seems like Python has no easy way
to prefix flags before the rest.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}