libc++ tests: compare.pass test redesign

Hello,

I have a problem with one of the libc++ tests and would greatly appreciate if you could clarify.

The test is: libcxx/test/std/localization/locale.categories/category.collate/locale.collate.byname/compare.pass.cpp.

It sets different locales and compares 2 strings "aaaaaaA" and "BaaaaaA" using std::collate::compare. The test expects the comparison result to be the same with every locale. This is not right. The result should be locale dependent as std::collate_byname uses strcoll_l/wcscoll_l. Implementation of these functions in the Apple C lib seems to be bogus, which makes the test pass there. Glibc doesn't have this bug, so XFAIL was added for linux-gnu.

As an experiment one can create two folders or files named "aaaaaaA" and "BaaaaaA" and run the following commands:
    LC_COLLATE=C ls
    LC_COLLATE=en_US.UTF-8 ls
Sort order will be different on Linux but the same on MacOs.

Besides, the test relies on the system locale as well (std::locale l("")) and expects a strictly defined comparison result, while the result actually depends on the system locale settings and not on the test itself.

Probably, the test should be overwritten to pass on Linux and XFAIL on platforms with bogus C lib.

Could you please review and share your opinion about this please?

Thank you in advance.
Oleg