pkg-config Requires.private and removal of static libraries

### Your question:

There has been a trend at conda-forge to remove static libraries and to split off runtime libraries from build time dependencies in order to save download space.

There has also been a combined trend to add `pkgconfig` files to enable more packages that were historically built only for linux, be able to get built for windows.

However, the inclusion of the `Requires.private` flag in the pkgconfig files makes it necessary to add back build time dependencies in order to "help the static builds" (see the last FAQ question in https://people.freedesktop.org/~dbn/pkg-config-guide.html)

I'm really not sure what to do about this. For example, many users have had to add back zlib as a host dependency (when their software doesn't link to it directly).

Second, the glib -> harfbuzz dependency is also a tough one to manage.

Thank you for your advice.

xref: https://github.com/conda-forge/zlib-feedstock/issues/69