autogen.sh: Honor NOCONFIGURE environment variable

See http://people.gnome.org/~walters/docs/build-api.txt

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/autogen.sh b/autogen.sh
index c76bf8b..b5f6ec4 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -15,4 +15,6 @@
 
 autoreconf -v --install || exit 1
 
-"$srcdir"/configure "$@"
+if test -z "$NOCONFIGURE"; then
+    "$srcdir"/configure "$@"
+fi