[PATCH] [Sema] Re-land "Make FunctionType's TSI use unadjusted argument types"

[Eli Friedman]

  At a higher level, the big, potentially breaking change here is that you're making FunctionProtoType::getArgType() potentially return an undecayed type.  There are around 100 users of this API in-tree, and it looks like a substantial fraction of them are going to need a similar change.  I'm not comfortable with an API named getArgType() returning an un-decayed type; even if you catch all the existing cases which need additional checks, people writing new code aren't going to be thinking about this, and the un-decayed type is almost always the wrong answer from a semantic point of view.  Any APIs on FunctionProtoType returning un-decayed types should have "un-decayed" in the name, IMO.

http://llvm-reviews.chandlerc.com/D957