[gtk+] Use AM_DISTCHECK_CONFIGURE_FLAGS

[Matthias Clasen <matthiasc src gnome org>]

commit 6faafbff6eab8992ef226ba40ca895876698b47d
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Mar 30 21:54:04 2016 -0400

    Use AM_DISTCHECK_CONFIGURE_FLAGS
    
    This is preferred over DISTCHECK_CONFIGURE_FLAGS in modern automake.

 Makefile.am |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index a4c56a7..38e8b1c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -95,7 +95,7 @@ ChangeLog:
 uninstall-local:
        rm -f $(DESTDIR)$(pkgconfigdir)/gtk+-3.0.pc
 
-DISTCHECK_CONFIGURE_FLAGS =            \
+AM_DISTCHECK_CONFIGURE_FLAGS =         \
        --enable-gtk-doc                \
        --disable-doc-cross-references  \
        --enable-man                    \