[gdm] (3 commits) Non-fast-forward update to branch wip/nielsdg/remove-other-headers

[Ray Strode <halfline src gnome org>]

The branch 'wip/nielsdg/remove-other-headers' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  6b87033... configure.ac: remove libgen.h check.

Commits added to the branch:

  a2e255b... configure.ac: Remove execinfo.h check. (*)
  54cac35... Merge branch 'wip/nielsdg/remove-execinfo' into 'master' (*)
  9140e0c... configure.ac: remove libgen.h check.

(*) This commit already existed in another branch; no separate mail sent