swift234

Pull libswiftStdlibStubs.a, libswiftRuntime.a into libswiftCore.a

libswiftStdlibStubs.a is meant to be an intermediate built product
that's pulled into libswiftCore.a, not its own thing. Add a post-build
step for libswiftCore.a to pull all the object files into it from
libswiftStdlibStubs.a.

(Also, be careful only to do this for private link libraries that are
actually targets.)

<rdar://problem/23621157>