swift234

Move PassManager related code into the PassManager directory in order to prevent layering issues with sublibraries of SILPasses that may depend on it.

I am doing this so that I can move the SILCombiner code into its own
subdirectory. Without this, we have the new SILCombiner library depending on
symbols in SILPasses but yet SILPasses also depends on the SILCombiner code.

Swift SVN r32331