[mutter] configure: Explicitly require gl pkgconfig file

[Carlos Garnacho <carlosg src gnome org>]

commit 64cb735abf83d876abeb7f6f9cc601f2908b50c2
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Oct 9 13:41:41 2017 +0200

    configure: Explicitly require gl pkgconfig file
    
    Mutter now does direct calls to GL, so we should add the requirement to
    it. Fixes underlinking when generating Meta-1.gir.

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index a5870e6..c7b2651 100644
--- a/configure.ac
+++ b/configure.ac
@@ -80,6 +80,7 @@ CANBERRA_GTK_VERSION=0.26
 LIBWACOM_VERSION=0.13
 
 MUTTER_PC_MODULES="
+   gl
    egl
    gtk+-3.0 >= 3.19.8
    gio-unix-2.0 >= 2.35.1