[swift-build-dev] Draft proposal: "Test Executables"

[George King]

> I agree with Ankit that it probably makes sense to add them both in one go. Your motivation partially applies here w.r.t. consistency in the matrix of supported options, the only additional bit of motivation for libraries is that test targets may want to share code in a place clearly distinguished from the package's product libraries -- thats similar to the motivation for not putting the test libraries in with Sources.
> 
> Aside from that, the proposal LGTM. I don't really think anything is needed for detailed design, this is just extending the existing convention.
> 
> If no one else has feedback before, say, Thursday, and you are willing to add the bit above, I can serve as review manager for this over next week if you make a PR against swift-evolution and cc me on it.

That's great. I'll fix it up to read as 'Test Libraries and Executables'.