AFAIK they are not intended to be installed as compiled code at all.
You are supposed to bundle them, or otherwise compile them from sources
along with your project.

You are correct, apparently they changed their stance on this some time ago as you can read here:

https://github.com/google/googletest/blob/master/googletest/docs/FAQ.md#why-is-it-not-recommended-to-install-a-pre-compiled-copy-of-google-test-for-example-into-usrlocal

They also no longer support the autotools scripts that are provided with the source code as you can read in the README:

https://github.com/google/googletest/blob/master/googletest/README.md#legacy-build-scripts

There are quite some packages depending on them so they can't just be last-rited. Maybe the best solution is to leave them in their current form (perhaps update the SRC_URI) and not accepting package updates to 1.8, instead asking upstream packages that depend on them to include them in their source distribution.

br,

Mathy