Allow compilation of C/C++/ObjC/ObjC++ files with module from TH

The main goal is to easily allow the inline-c project (and
similar projects such as inline-java) to emit C/C++ files to
be compiled and linked with the current module.

Moreover, `addCStub` is removed, since it's quite fragile. Most
notably, the C stubs end up in the file generated by
`CodeOutput.outputForeignStubs`, which is tuned towards
generating a file for stubs coming from `capi` and Haskell-to-C
exports.

Reviewers: simonmar, austin, goldfire, facundominguez, dfeuer, bgamari

Reviewed By: dfeuer, bgamari

Subscribers: snowleopard, rwbarton, dfeuer, thomie, duncan, mboes

Differential Revision: https://phabricator.haskell.org/D3280