Print struct return functions and calls as actually returning the hidden

Print struct return functions and calls as actually returning the hidden
argument struct pointer, enabling ABI compatibility for the CBE with
platforms with strange struct-return ABIs.  This fixes 252.eon and
CoyoteBench/fftbench on Darwin/X86 among other things.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28442 91177308-0d34-0410-b5e6-96231b3b80d8