Some of the dependencies' build systems for Visual Studio do not provide a
pkg-config file upon build, so we use find_library() for them when the
corresponding pkg-config files are not found during Visual Studio builds,
so that one will not need to make up pkg-config files for them, which
could be error-prone.  These .lib names match the names that are built
with the officially supported build system that is used by their
respective Visual Studio support.

For ZLib, this will make gio-2.0.pc reflect on the zlib .lib based on
what is found, or whether we use the fallback/bundled ZLib, when we
don't have a pkg-config file for ZLib on MSVC.  We still need to depend
on Meson to be updated to put the correct link argument for linking ZLib
in the pkg-config case.

https://bugzilla.gnome.org/show_bug.cgi?id=783270