pkgconfig: add uuid.pc

[tschoonj]

The util-linux uuid library is provided by macOS, through its header at
/usr/include/uuid/uuid.h, and implementation included in libSystem.B.dylib
Using this it is possible to reduce dependency on the unmaintained ossp-uuid formula in a couple of cases.

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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[tschoonj]

Are unit tests necessary for this kind of change?

[MikeMcQuaid]

Are unit tests necessary for this kind of change?

Nope! Looks good, thanks again @tschoonj!