Push the top level logic for writing out swiftmodules and associated files into the frontend library which has access to all the necessary dependencies.
Eventually this will include both modules and source files that the
emitted module depends on, but for now it's just going to be used for
testing purposes to forward to normal source loaders.
Swift SVN r5108
Alternately, "add a system of ridiculous overkill for bitcode record layout",
in the spirit of DRY over YAGNI. It /is/ much more concise than the LLVM way.
Use this to emit a sketch of Clang's PCH control block, although nothing's in
there yet besides "version 1.0" and the LLVM revision number; the latter is
more "proof of concept" than actually useful. We should figure out a good
way to identify trunk Swift compilers; this shouldn't be difficult.
Swift SVN r5107
