Prevent general tests from running while running benchmarks custom target

[chapman39]

Issue

It is expected only benchmarks should run when executing make run_benchmarks.

The configuration -C option in add_custom_target prevents benchmarks from running while executing make test. However, all tests and benchmarks run while executing make run_benchmarks.

This PR

Adds a "Benchmark" label -L. This means now only benchmarks will run during make run_benchmarks. And make test remains to only run general tests, no benchmarks.

[kennyweiss]

Thanks @chapman39 !

Are there any docs to update? Or does this fall under general CMake usage?

[kennyweiss]

Thanks!

[white238]

Thanks @chapman39 !