[Bug libstdc++/83626] std::experimental::filesystem::remove_all throws exception instead of returning 0 if path doesn't exist

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83626

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Christophe Lyon from comment #10)
> In my testing, I have a new failure:
> FAIL:: experimental/filesystem/operations/remove.cc execution test
> on aarch64-linux-gnu and arm*linux* targets.
> 
> I'm cross-testing using proot+qemu, so maybe there is a bad interaction.
> 
> The log says:
> /libstdc++-v3/testsuite/experimental/filesystem/operations/remove.cc:81:
> void test01(): Assertion 'ec' failed.

This means that remove(3) can remove a directory below a directory with mode
000.

I'll adjust the test to account for such cases.