Make promoteOp work for CT*

Proof?

ubyte %bar(ubyte %x) {
entry:
        %tmp.1 = call ubyte %llvm.ctlz( ubyte %x )
        ret ubyte %tmp.1
}

==>

zapnot $16,1,$0
CTLZ $0,$0
subq $0,56,$0
zapnot $0,1,$0
ret $31,($26),1

llvm-svn: 21691