[mutter] build: Add missing file

[Florian Müllner <fmuellner src gnome org>]

commit ff5a7ba9b9ea3c1ce1851ef0a9a3fb1404f1a7b6
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Nov 23 22:20:32 2016 +0100

    build: Add missing file

 src/Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index ab5a26c..15f6077 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -93,6 +93,7 @@ libmutter_la_SOURCES =                                \
        backends/meta-cursor-renderer.h         \
        backends/meta-egl.c                     \
        backends/meta-egl.h                     \
+       backends/meta-egl-ext.h                 \
        backends/meta-display-config-shared.h   \
        backends/meta-idle-monitor.c            \
        backends/meta-idle-monitor-private.h    \