aarch64: directory location for BTI and GCS tests

[Florian Weimer]

* Yury Khrustalev via Libc-help:

> I've realised that there is a bit of inconsistency in where we have
> tests for BTI and GCS added over the recent months. The BTI tests are
> in the "sysdeps/aarch64" folder and the GCS tests have been put into
> the "sysdeps/unix/sysv/linux/aarch64" folder.
>
> Since all these tests are using HWCAP and rely on the prctl() syscall,
> I believe the right place for all such tests would in the corresponding
> folder "sysdeps/unix/sysv/linux/aarch64". Does this make sense?

I would say so.  PAC could be considered generic because it's not
process-switched, but the reset is Linux-specific for now.

> If I refactor location of the tests, I think it would also be useful to
> place them in separate directories. However, it seems that the de facto
> convention is to have all tests in the root of a respective directory
> without and sub-folder structure. Is this intentional?

There is no component-based subdirectory structure under sysdeps.
Subdirectories appear due to relative includes or the Implies mechanism.
Component directories are handled via $(subdir) conditionals in the
Makefile for the directory.  It's a bit awkward.

Thanks,
Florian