bug#62450: 29.0.60; Skip failing tests on Cygwin with native compilation

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 25 Mar 2023 16:55:49 -0400
> From: Ken Brown <kbrown@cornell.edu>
> 
> When 'make check' is run on Cygwin and Emacs has been built with native
> compilation, all the tests in comp-tests.el and benchmark-tests.el fail
> with fork errors, for the reasons explained in etc/PROBLEMS.  I don't
> see an easy way to fix this by rebasing, as is done elsewhere in the
> code, and I don't think it's worth investing any effort into this just
> for the sake of making some tests pass.  I propose that we just skip
> these tests.
> 
> Patch attached (with a placeholder for the bug number).  OK for emacs-29?

OK, but please add in both places comments explaining the reason, and
in particular include there a pointer to etc/PROBLEMS.

(I do wonder whether this is a good idea in the long run.  Native
compilation is here to stay, so avoiding its testing for Cygwin might
not be the best solution.  The PROBLEMS entry seems to imply that
relatively simple measures, which the test suite could take, could
avoid the fork failures, so my recommendation would be to try to find
a better fix in the future, albeit not in Emacs 29.)