zstd headers?

[Tobias Nygren <tnn%NetBSD.org@localhost>]

Hi,

So this started with me wanting to add zstd support to pkg_create -F to
evaluate if that could enhance pkg_add performance in bulk builds.

like with xz, we only reasonably want to enable zstd in pkgsrc's
pkg_install if it is an OS builtin. NetBSD ships with the zstd shlib
but not the headers nor the pkg-config file so applications cannot use
it and a builtin.mk in pkgsrc would not detect it even if added.

The header is in the comp flist but was marked obsolete.
I'm not sure of the reason hence opening this thread for discussion.

Kind regards,
-Tobias