For local variables in functions with a frame pointer, use FP as a base

For local variables in functions with a frame pointer, use FP as a base
register for local access when it's closer to the stack slot being refererenced
than the stack pointer. Make sure to take into account any argument frame
SP adjustments that are in affect at the time.

rdar://8256090

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110366 91177308-0d34-0410-b5e6-96231b3b80d8