Generate and install the pkg-config file on Windows

[pkgw]

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [x] Bumped the build number (version is unchanged)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

This edits the Windows MSVC build to generate and install the pkg-config file, which is normally only activated for Unix or Cygwin. This is motivated by conda-forge/libtiff-feedstock#80, where version 4.4 of libtiff changes its pkg-config file to reference a libzstd.pc that doesn't currently exist on Windows. This was in turn discovered in conda-forge/librsvg-feedstock#96, which is currently stuck due to the libtiff update.

After applying this patch, and conda-forge/jpeg-feedstock#36, I can confirm that librsvg starts building again on my test machine.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[pkgw]

@conda-forge-admin, please rerender

[hmaarrfk]

Can you expand the test as well?