Resolve implicit alignment before computing the FoldingSet information so

Resolve implicit alignment before computing the FoldingSet information so
that the CSE map always contains explicit alignment information. This allows
more loads to be CSE'd when there is a mix of explicit-alignment loads and
implicit-alignment loads.

Also, in SelectionDAG::FindModifiedNodeSlot, add the operands to the
FoldingSetNodeID before the load/store information instead of after, so
that it matches what is done elsewhere.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37411 91177308-0d34-0410-b5e6-96231b3b80d8