[Sparc] Rewrite MBB's live-in registers for leaf functions. Also, add
register i7 as a live-in if current function's return address is taken.

This revision fixes PR16269.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187433 91177308-0d34-0410-b5e6-96231b3b80d8