build: Skip configure step if is NOCONFIGURE set

Allow users of autogen.sh to skip the call to configure, which is needed
when building out of tree.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
diff --git a/autogen.sh b/autogen.sh
index 629a257..ec633f3 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -16,4 +16,6 @@
 autoreconf -v --install || exit 1
 cd $ORIGDIR || exit $?
 
-$srcdir/configure "$@"
+if test -z "$NOCONFIGURE"; then
+        $srcdir/configure "$@"
+fi