[mutter] build: Adjust to filename changes

[Florian Müllner <fmuellner src gnome org>]

commit e34c330f660ea7bdc869b8c731d703892833a4e0
Author: Florian Müllner <fmuellner gnome org>
Date:   Mon May 7 22:25:30 2018 +0200

    build: Adjust to filename changes
    
    The meta-stage and meta-window-group headers got split into a public
    and private part, but the Makefiles still reference the old files.

 src/Makefile.am | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index 59108c069..bcb3505c7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -153,7 +153,7 @@ libmutter_@LIBMUTTER_API_VERSION@_la_SOURCES =      \
        backends/meta-pointer-constraint.h      \
        backends/meta-settings.c                \
        backends/meta-settings-private.h        \
-       backends/meta-stage.h                   \
+       backends/meta-stage-private.h           \
        backends/meta-stage.c                   \
        backends/meta-renderer.c                \
        backends/meta-renderer.h                \
@@ -246,7 +246,7 @@ libmutter_@LIBMUTTER_API_VERSION@_la_SOURCES =      \
        compositor/meta-window-actor.c          \
        compositor/meta-window-actor-private.h  \
        compositor/meta-window-group.c          \
-       compositor/meta-window-group.h          \
+       compositor/meta-window-group-private.h  \
        compositor/meta-window-shape.c          \
        compositor/region-utils.c               \
        compositor/region-utils.h               \