zstd: clean up template.

[leahneukirchen]

The zstd template had multiple issues:

• Since not all targets where built in do_build, compilation happened in do_install.
• Both zstd(1) and pzstd(1) statically linked libzstd.
• The libzstd.a library was meant to have multi-threading support, but was overwritten by a single-threaded version as a side-effect.

We patch pzstd to use dynamic linking and use "zstd-dll" for zstd.

In the future we may want to consider using cmake or ninja, but as it's a bootstrap package I've kept it on make.

[sgn]

We can use cmake build-style because that one use cmake-bootstrap, which vendored their own version of libzstd;
and either:

• split the build for bootstrap; or
• require cmake in bootstrap (foreign) environment

[sgn]

Ah, cmake can find its modules by relative path, too. I may look into add cmake-bootstrap to the bootstrap path.

[leahneukirchen]

AFAICS nothing else uses cmake yet, so let's stick to the Makefile for now?

[sgn]

1.5.5 doesn't support cmake yet,anyway. So, we must stick with Makefile. There's ccache that uses cmake, but we delayed it until stage1

[leahneukirchen]

it does (also ninja): https://gitlab.archlinux.org/archlinux/packaging/packages/zstd/-/blob/main/PKGBUILD?ref_type=heads#L35