[InstCombine] Make x86 PADDS/PSUBS constant folding tests generic

As discussed on D55894, this replaces the existing PADDS/PSUBUS intrinsics with the the sadd/ssub.sat generic intrinsics and moves the tests out of the x86 subfolder.

PR40110 has been raised to fix the regression with constant folding vectors containing undef elements.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349759 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed