[SelectionDAG] Add AssertAlign to AddNodeIDCustom so that it will CSE properly.

The alignment needs to be part of the folding set hash. This is
handled by getAssertAlign when nodes are created, but needs to repeated here.

No test case as I found it as part of a very early experimental patch.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D122279