[InlineFunction] Handle return attributes on call within inlined body

[InlineFunction] Handle return attributes on call within inlined body

Consider a callee function that has a call (C) within it which feeds
into the return.  When we inline that callee into a callsite that has
return attributes, we can backward propagate those attributes to the
call (C) within that inlined callee body.

This is safe to do so only if we can guarantee transfer of execution to
successor in the window of instructions between return value (i.e. the
call C) and the return instruction.

See added test cases.

Reviewed-By: reames, jdoerfert
Differential Revision: https://reviews.llvm.org/D76140