BUG: Fix test_ccompiler_opt when path contains dots

[mgorny]

Fix test_ccompiler_opt not to be confused by dots occurring on the path
to the temporary directory, by using only the source file's basename
when grabbing options. Otherwise, the test can fail with mismatches
such as:

E           AssertionError: 'sources_status' returns different targets than the compiled targets
E           ['AVX512F', 'AVX2'] != ['(20 2/TEMP/TMPB0YHSCAI/TEST_TARGETS AVX512F)', '(20 2/TEMP/TMPB0YHSCAI/TEST_TARGETS AVX2)']

This is because our TMPDIR value includes numpy version, i.e. 1.20.2.
The splitting happens on the first dot that is part of the directory
path rather than test filename.

[mattip]

@seiko2plus thoughts?

Is there a better way to get the gtar feature than to fetch it from the file name?

[seiko2plus]

@mattip,

Is there a better way to get the gtar feature than to fetch it from the file name?

No, the other way would be parsing the generated C header config of the dispatch-able source to get the generated targets.

[seiko2plus]

Well done, Thank you!