swift234

Select ABI types for all arguments of a C/ObjC function together.

Updates to signature expansion, entrypoint lowering, and callsite
lowering so that each selects the ABI types for all arguments at once
rather than an argument at a time (as well as considering whether the
return value is returned indirectly). This is required to get the
correct behavior in cases where we run out of argument registers and
need to pass arguments as indirect byvals.

This is mostly just refactoring existing code to move loops inside inner
functions as well as dealing with return values at the same time as
arguments.

Swift SVN r13781