Large tuples of values (e.g char[32]) can be passed directly at the abi
boundry but expand to a big explosion of values.
Peephole this explosion at argument passing and return value passing
points to avoid code size growth associated with the explosion.
Use the generic type lowering algorithm described in
"docs/CallingConvention.rst#physical-lowering" to map from IRGen's explosion
type to the type expected by the ABI.
Change IRGen to use the swift calling convention (swiftcc) for native swift
functions.
Use the 'swiftself' attribute on self parameters and for closures contexts.
Use the 'swifterror' parameter for swift error parameters.
Change functions in the runtime that are called as native swift functions to use
the swift calling convention.
rdar://19978563
