[gnome-builder] templates: fix autogen.sh with '--enable-gtk-doc'

[Christian Hergert <chergert src gnome org>]

commit 637a5b148ac9f53de1b8231a5cdb4e31cb3055ea
Author: Mohammed Sadiq <sadiq sadiqpk org>
Date:   Sun Feb 26 17:04:10 2017 +0530

    templates: fix autogen.sh with '--enable-gtk-doc'
    
    an m4 directory is required for gtkdocize to work
    
    https://bugzilla.gnome.org/show_bug.cgi?id=779221

 .../autotools_templates/resources/autogen.sh       |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/plugins/autotools-templates/autotools_templates/resources/autogen.sh 
b/plugins/autotools-templates/autotools_templates/resources/autogen.sh
index 8f3189e..11d1d5f 100644
--- a/plugins/autotools-templates/autotools_templates/resources/autogen.sh
+++ b/plugins/autotools-templates/autotools_templates/resources/autogen.sh
@@ -22,6 +22,8 @@ if [ "$#" = 0 -a "x$NOCONFIGURE" = "x" ]; then
        echo "" >&2
 fi
 
+mkdir -p m4
+
 {{if enable_gtk_doc}}
 gtkdocize || exit 1
 {{end}}