Fix GObject introspection for x86, Windows

[jwahlstrand]

Currently the generation scripts are being run on my computer with GObject introspection installed as part of the distribution, and the introspection is being done on the distribution's versions of GTK, etc. This works fine for x64, but for x86 some of the argument types are wrong because size_t is different. On Windows, a few types in GLib (really just GIO) don't exist, but these can be skipped.

It would be great (and more correct) if we could include the typelib files in the JLL's. We could shift generation to a build step or at least guarantee that the introspected data is consistent with the library versions being used. As a first step toward this, I compiled gobject-introspection using BInaryBuilder for linux-x86_64-musl. It's in https://github.com/jwahlstrand/Yggdrasil in a branch "gi".

It turns out that cross-compiling gobject-introspection is hard, particularly on a platform that uses musl. This is a potentially useful resource:

https://maxice8.github.io/8-cross-the-gir/

[giordano]

For the record, inside the BinaryBuilder environment you can ran any pure C code built for {x86_64,i686}-linux-{gnu,musl}, not just x86_64-linux-musl.