X86: Avoid accessing SDValues after they've been RAUW'd

This fixes two use-after-frees in selectLEA64_32Addr. If matchAddress
matches an ADD with an AND as an operand, and that AND hits one of the
"heroic transforms" that folds masks and shifts, we end up with N
pointing to an SDNode that was deleted. Make sure we're done accessing
it before that.

Found by ASan with the recycling allocator changes in llvm.org/PR26808.

llvm-svn: 266130