With https://github.com/msys2/msys2-autobuild/commit/dc632d99340da8b204fa2d7
we can now override COMPRESSZST in autobuild, to use higher than default
compression when building packages for the repo.
This means we can revert the default COMPRESSZST back to the default
zstd compression level (3) and make packaging faster for development/CI
etc.
This is motivated by https://github.com/msys2/MINGW-packages/pull/20591
where flang v18 stopped supporting the -pipe flag which is passed to
it via LDFLAGS. v17 still supported it and it's not clear where and when
it was changed exactly.
Let's remove it from LDFLAGS because:
* it's not clear if -pipe actually does anything for linking
(it's still passed via CFLAGS/CXXFLAGS)
* other distros like Arch/Gentoo also only add it to CFLAGS/CXXFLAGS
* of the above flang issue
* Add a dependency on zstd so that makepkg can use it
* Remove the upx option from the config because it was removed
in pacman: https://git.archlinux.org/pacman.git/commit/?id=1a29744d0d
* Various other syncs and adjustments for zstd
.. in the face of using `git am` to apply patches.
We set `GIT_COMMITTER_NAME` and `GIT_COMMITTER_EMAIL` to fixed
values and provide a `gitam_mkpkg` function that passes
`--committer-date-is-author-date`
The means we can generate packages with the same, correct sha1
without needing to mess about with `git reset` (and thus getting
the old sha1 before our patches were applied).
Also, removed the `-j1` from make since it doesn't seem to be
needed anymore. Perhaps upstream fixed a race condition?
