gen_makefile: allow combining several .opts files
diff --git a/default.opts b/default.opts
new file mode 100644
index 0000000..e79879f
--- /dev/null
+++ b/default.opts
@@ -0,0 +1,2 @@
+osmo-msc --enable-smpp
+osmo-bsc --enable-osmo-bsc --enable-nat