Draft: pkg-config.recipe: Make it a runtime dep on all platforms

It was supposed to be a runtime dep on Windows, but because we had the same recipe twice inside the recipes/ dir, only the first one was being parsed, so it was not a runtime dep even when we previously wanted it to be.

By making it a runtime dep everywhere, we're ensuring that it is built as the very first thing when building anything. This unfortunately means that the recipe will be built twice: once in bootstrap and then again in package.

Even more unfortunately, we actually need that because we need to ship the built pkg-config in our binary releases. For instance, because people that consume the built binaries need a pkg-config (because macOS and Windows do not ship it) or they need a pkg-config that defaults to --define-prefix (on Linux).

Fixes #346 (closed)

Draft because building pkg-config with Autotools on Windows is really slow, and I'm not sure if we want to take that hit. Need to measure the impact with MSYS2 and make a call on whether to port it to Meson or switch to pkgconf. Porting to Meson is non-trivial because it requires building the internal glib copy, but that just requires someone to copy things from the glib Meson files.