[mutter] build: Fix gtk-doc build failure when native backend is disabled

[Ting-Wei Lan <lantw src gnome org>]

commit 0bfebc3cae77729d20b887025158c661233b6083
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Mon Jan 19 20:09:39 2015 +0800

    build: Fix gtk-doc build failure when native backend is disabled
    
    https://bugzilla.gnome.org/show_bug.cgi?id=743173

 doc/reference/Makefile.am |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/doc/reference/Makefile.am b/doc/reference/Makefile.am
index 6794e96..cae0b85 100644
--- a/doc/reference/Makefile.am
+++ b/doc/reference/Makefile.am
@@ -115,8 +115,10 @@ IGNORE_HFILES= \
 if !HAVE_NATIVE_BACKEND
 IGNORE_HFILES+= \
        meta-backend-native.h \
+       meta-barrier-native.h \
        meta-cursor-renderer-native.h \
        meta-idle-monitor-native.h \
+       meta-input-settings-native.h \
        meta-monitor-manager-kms.h \
        $(NULL)
 endif