[DAGCombiner] (add (umax X, C), -C) --> (usubsat X, C) (PR40111)

Move the (add (umax X, C), -C) --> (usubsat X, C) X86 combine into generic DAGCombiner

First of a number of saturated arithmetic folds that can be moved out of X86-specific code for PR40111.

Differential Revision: https://reviews.llvm.org/D57754

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353457 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed