[clutter-gtk] build: Fix gtk-doc build when builddir != srcdir

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

commit 6cf40d8f5837c73e7a0589b306ae33c760aadc1d
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Tue Jun 14 10:26:54 2016 +0800

    build: Fix gtk-doc build when builddir != srcdir
    
    https://bugzilla.gnome.org/show_bug.cgi?id=767627

 doc/reference/Makefile.am |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/doc/reference/Makefile.am b/doc/reference/Makefile.am
index 939e696..92125bf 100644
--- a/doc/reference/Makefile.am
+++ b/doc/reference/Makefile.am
@@ -74,7 +74,7 @@ expand_content_files=
 # e.g. INCLUDES=-I$(top_srcdir) -I$(top_builddir) $(GTK_DEBUG_FLAGS)
 # e.g. GTKDOC_LIBS=$(top_builddir)/gtk/$(gtktargetlib)
 
-AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir) $(CLUTTER_GTK_DEPS_CFLAGS)
+AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir) -I$(top_builddir)/clutter-gtk $(CLUTTER_GTK_DEPS_CFLAGS)
 GTKDOC_LIBS=$(top_builddir)/clutter-gtk/libclutter-gtk-$(CLUTTER_GTK_API_VERSION).la $(CLUTTER_GTK_DEPS_LIBS)
 
 # This includes the standard gtk-doc make rules, copied by gtkdocize.