Fix calls that need to store values in stack slots, to not copy the stack

pointer.  This allows us to emit stuff like this:

        li r10, 0
        stw r10, 56(r1)
        or r3, r10, r10
        or r4, r10, r10
        or r5, r10, r10
        or r6, r10, r10
        or r7, r10, r10
        or r8, r10, r10
        or r9, r10, r10
        bl L_bar$stub

instead of this:

        or r2, r1, r1     ;; Extraneous copy.
        li r10, 0
        stw r10, 56(r2)
        or r3, r10, r10
        or r4, r10, r10
        or r5, r10, r10
        or r6, r10, r10
        or r7, r10, r10
        or r8, r10, r10
        or r9, r10, r10
        bl L_bar$stub

wowness.

llvm-svn: 25221