Ensure HAVE_SETRES{GID,UID} are set and remove hack for undefined symbols

This commit remove the hack previously added by commit bfbc54993e.

Thanks to @patmarion for reporting the issue.
Merge branch 'fix-setresgid-setresuid-undefined-symbol' into next

* fix-setresgid-setresuid-undefined-symbol:
  Ensure HAVE_SETRES{GID,UID} are set and remove hack for undefined symbols