t/unit-tests: handle dashes in test suite filenames

t/unit-tests: handle dashes in test suite filenames

"generate-clar-decls.sh" script is designed to extract function
signatures that match a specific pattern derived from the unit test
file's name. The script does not know to massage file names with dashes,
which will make it search for functions that look like, for example,
`test_mem-pool_*`. Having dashes in function names is not allowed
though, so these patterns won't ever match a legal function name.

Adapt script to translate dashes (`-`) in test suite filenames to
underscores (`_`) to correctly extract the function signatures and run
the corresponding tests. This will be used by subsequent commits which
follows the same construct.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Seyi Kuforiji <kuforiji98@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>