runtime(syntax-tests): Re-introduce support for "phoney" languages

runtime(syntax-tests): Re-introduce support for "phoney" languages

As of patch v9.1.1176~1, there are no longer makeshift Make
targets to accommodate language names that can match phoney
targets.  For example, "clean_" was previously generated for
Clean because otherwise it clashed with the "clean" target.

Additionally, enable test filtering for makeshift targets.

Reference:
https://wiki.clean.cs.ru.nl/Clean

closes: #16810

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>