Half of the ports had a manual post_install step to delete libtool files
this is now done automatically and there is no need for it!
Libtool files have to be deleted as libtool doesn't work while
cross-compiling (at least out of the box)
binutils uses pkg-config to find zstd for the host when building. If our
zstd port is installed, it finds it instead and ends up including our
own sysroot which is incompatible with host's.
unsetting pkg-config related variables fixes this and allows binutils to
build fine even when zstd is installed. We can now make it a dependency.
Bananymous