Add pkgconfig metadata on windows

[h-vetinari]

This would be useful to be able to run test for pkgconfig-metadata in dependent repos, e.g. grpc-cpp, c.f. conda-forge/grpc-cpp-feedstock#239

Content is taken from https://github.com/microsoft/vcpkg/blob/master/ports/openssl/install-pc-files.cmake and cross-referenced with our own pkgconfig files on unix (from where I took the formatting).

[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.

[h-vetinari]

@hmaarrfk @isuruf
Any thoughts on this? I'd like to add tests for the pkg-config metadata on the grpc-cpp feedstock (not least if we're trying to remove private libs like zlib or abseil from the link interface), and had to disable this on windows because it fails to find openssl.pc.

[hmaarrfk]

I'm a fan of the idea. I would just prefer not having m2 for now.

Can we simply use echo?

Less elegant than a template file maybe, but won't pull in a whole new stack.

[h-vetinari]

Less elegant than a template file maybe, but won't pull in a whole new stack.

Yes, agreed, but also... it's only during the build phase (so nothing in the final artefact)? Any specific concerns you have in mind?

[hmaarrfk]

Any specific concerns you have in mind?

Yes. I mostly fear that the build system will find some strange dependency and end up depending on m2

[h-vetinari]

@hmaarrfk PTAL :)

[hmaarrfk]

This looks good to me.