Fix build on GNU/Hurd

[sthibaul]

There is no path length limitation there, even via pathconf. But glibc
provides a getcwd function that allocates the buffer dynamically so we can
just leverage that.

[albert-github]

Thanks for pointing this out, though the file filesystem.hpp is an imported function from the https://github.com/gulrak/filesystem project (i.e. the file: https://github.com/gulrak/filesystem/blob/master/include/ghc/filesystem.hpp), so the problem should be reported upstream at the filseystem project as well.

[sthibaul]

Ok, submitted on gulrak/filesystem#154

[albert-github]

I see that the fix gulrak/filesystem#154 has been integrated in the master version on https://github.com/gulrak/
I just created an issue about the plans for a new release gulrak/filesystem#164

[albert-github]

I see that the new release of filesystem is out for some time and that it has been integrated in the doxygen master as well.
So do you still have the same problems when using the master version of doxygen or has this been solved now?
Actually I think this PR can be closed as fixed upstream.

[doxygen]

This issue was previously marked 'fixed but not released',
which means it should be fixed in doxygen version 1.9.7.
Please verify if this is indeed the case. Reopen the
issue if you think it is not fixed and please include any additional information
that you think can be relevant (preferably in the form of a self-contained example).