When doing address-mode sinking, expand the base register first, rather

When doing address-mode sinking, expand the base register first, rather
than the scaled register. This makes it more likely that subsequent
AddrModeMatcher queries will match the new address the same way as the
old, instead of accidentally matching what had been the base register
as the new scaled register, and then failing to match the scaled register.
This fixes some problems with address-mode sinking multiple muls into a
block, which will be a lot more common with some upcoming
LoopStrengthReduction changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93935 91177308-0d34-0410-b5e6-96231b3b80d8