Make our windows builds usable from meson.

This creates our pkg-config files on windows as well as fixes an include in
pidgin.h which can cause some issues.

This isn't usable as is, as you need a machine-file and a pkg-config wrapper
to make this all work, but that will be updated in the win32-dev.7z file thats
on data.imfreedom.org.

Testing Done:
Compiled guifications2 (which now uses meson) on windows and verified it works.

Reviewed at https://reviews.imfreedom.org/r/615/