how to specify a default configuration in a library's dub.json? (i.e if the use doesn't not have subConfigurations)

[mw]

I think the reason for the library build failure is, it directly 
calls dmd instead of dub to build the library:

dmd -oflibthriftd-ssl.a -w -wi -Isrc -lib src/thrift/async/ssl.d 
src/thrift/internal/ssl.d ...


So my next question is what should be the correct dmd equivalent 
of the dub command?