If -nsstring-is-string is enabled, lower Strings in cc(c) and cc(objc) function types to NSString, and when calling them, insert calls to StringToNSString/NSStringToString to perform the bridging conversion.
This isn't quite ready for prime-time yet, because we still need to emit the inverse bridging for ObjC method thunks, and I haven't tested the IRGen end of things yet.
Swift SVN r5355
Generate and cache SILFunctionTypeInfo from Swift types on the fly, and simplify the SILType representation down to a CanType and isAddress bit.
Swift SVN r5298
This frees up an extra bit in SILType, which we can expose to LLVM through
PointerLikeTypeTraits. Use this bit in a PointerUnion, which allows simplifying
ValueBase, which happened to be the last use of the isInvalid() state.
Swift SVN r5218
