Add pthread-stubs as a runtime dependency

[pkgw]

Without including this, every single package that does a pkg-config check for the xcb module needs to remember to pull in pthread-stubs as a dependency: XCB's pkg-config file requires pthread-stubs.pc and pkg-config checks will fail if the latter isn't available. This is admittedly a secondary use case, but this problem keeps on biting me, and it can cause subtle failures because problems happen even when a package only depends implicitly on libxcb.

Ideally, instead of this, we'd start having -devel packages and/or dev-only dependencies, but conda-build and conda-forge are a long ways away from that. The extra package to install is annoying but it contains literally just the one pkg-config file.

Alternatively one could start bundling pthread-stubs.pc in with this package, but the standalone package already exists (in defaults too) so I feel that it's better to just go ahead and use it.

Checklist

• [x] Used a fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [x] Reset the build number to 0 (if the version changed)
• [x] Re-rendered with the latest conda-smithy
• [x] Ensured the license file is being packaged.

[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.

[ccordoba12]

Quick question (out of curiosity): what other packages (besides Qt) require xcb?

[pkgw]

@ccordoba12 cairo now does on Linux, since using our X.org packages seemed to be the best path towards getting it building successfully on conda-build 3. That's probably the big one.

I build gtk3 packages that end up depending on it too, but those aren't in conda-forge.

[pkgw]

This PR now also fixes the Windows package. These two issues could be dealt with separately — but I would like to see the original change merged, if there are no objections.