Separate cmake coverage logic and resolve clang support issue

[skliper]

Is your feature request related to a problem? Please describe.
-pg option is not supported by clang in OS X 10.9 and later

Describe the solution you'd like
Consider a coverage.cmake implementation similar to the example: https://github.com/StableCoder/cmake-scripts.

See comments on #403... (really relating to #404).

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC

[astrogeco]

Adding some more cases here:
the -pg option is not supported by musl-libc used in some linux distros like Alpine