build: Add fallback dependency discovery for MSVC

build: Add fallback dependency discovery for MSVC

For dependencies that do not generate pkg-config files for their Visual
Studio build systems, we need to look for them using cc.has_header() and
cc.find_library(), namely for Cairo and HarfBuzz, if one does not have
crafted pkg-config files for them (which, by themselves may be
error-prone).

As a result, we will still try to look for Cairo and HarfBuzz using
pkg-config, but will give another shot at them on Visual Studio using
cc.has_header() and cc.find_library() if they couldn't be found via
pkg-config.

https://bugzilla.gnome.org/show_bug.cgi?id=785210