devel/google-cloud-cpp: Update to 2.27.0

Disable the mocking libraries, which require devel/googletest. This could
be a future optional feature, but not deemed needed at this time since
this is currently a leaf port. As mentioned in the release notes, not
linking the mocking libraries to GoogleTest was a bug that manifested
itself with CMake >= 3.30.0 [1].

Fix pkgconfig paths.

https://github.com/googleapis/google-cloud-cpp/releases/tag/v2.27.0

PR: 280381 [1], 280449
Approved by: portmgr (tcberner)