[libgd] Enable 'subdir-objects' automake option

[Christophe Fergeau <teuf src gnome org>]

commit edccd979ec13edbee1d0a52b48ed8589a265c85b
Author: Christophe Fergeau <cfergeau redhat com>
Date:   Tue Jun 24 23:32:50 2014 +0200

    Enable 'subdir-objects' automake option
    
    libgd's Makefile.am refers to source files in subdirectories, which
    causes warnings with automake 1.14. Enabling the 'subdir-objects'
    option silences these.
    
    libgd/Makefile.am:29: warning: source file 'libgd/gd-types-catalog.c' is in a subdirectory,
    libgd/Makefile.am:29: but option 'subdir-objects' is disabled
    automake: warning: possible forward-incompatibility.
    automake: At least a source file is in a subdirectory, but the 'subdir-objects'
    automake: automake option hasn't been enabled.  For now, the corresponding output
    automake: object file(s) will be placed in the top-level directory.  However,
    automake: this behaviour will change in future Automake versions: they will
    automake: unconditionally cause object files to be placed in the same subdirectory
    automake: of the corresponding sources.
    automake: You are advised to start using 'subdir-objects' option throughout your
    automake: project, to avoid future incompatibilities.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=732190

 Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 2816abf..8ccf38d 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,4 @@
+AUTOMAKE_OPTIONS=subdir-objects
 NULL =
 CLEANFILES =
 MAINTAINERCLEANFILES =