Use Linux functions on any OS based on GNU libc

[pinotree]

GNU libc (glibc) provides the prototypes for all the xattr functions.

Hence, extend the Linux support to anything based on GNU libc. In case of failures, most likely the underlying xattr functions will need to be fixed, rather than pyxattr itself.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.75%. Comparing base (e0cfe36) to head (7bb5bc7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #50   +/-   ##
=======================================
  Coverage   78.75%   78.75%           
=======================================
  Files           1        1           
  Lines         480      480           
  Branches       78       78           
=======================================
  Hits          378      378           
  Misses         63       63           
  Partials       39       39           

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[iustin]

Thanks! This looks sane, so approving.