[vala] (4 commits) Non-fast-forward update to branch wip/issue/745

[Rico Tzschichholz <ricotz src gnome org>]

The branch 'wip/issue/745' 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:

  3d5c94a... vala: Add Symbol.is_extern and use/set is accordingly
  8086b75... codegen: Don't write declaration of extern symbols with giv

Commits added to the branch:

  5966203... glib-2.0: Bind strcmp0 as GLib.CompareFunc<string?> (*)
  8f86bb7... xtst: Fix signature of XTest.fake_relative_motion_event() (*)
  b35b0b1... vala: Add Symbol.is_extern and use/set is accordingly
  70c4b16... codegen: Don't write declaration of extern symbols with giv

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