gen_makefile: allow combining several .opts files
diff --git a/transcoding.opts b/transcoding.opts
new file mode 100644
index 0000000..7147b5e
--- /dev/null
+++ b/transcoding.opts
@@ -0,0 +1,2 @@
+osmo-mgw --enable-mgcp-transcoding
+osmo-msc --enable-mgcp-transcoding