[X86][SSE] Remove use of SSE ADDS/SUBS saturation intrinsics from schedule/stack...

[X86][SSE] Remove use of SSE ADDS/SUBS saturation intrinsics from schedule/stack tests

These are due to be upgraded soon, but good to replace them with generic llvm sadd_sat/ssub_sat intrinsics now.

The avx512 masked cases need doing as well but require a bit of tidyup first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349621 91177308-0d34-0410-b5e6-96231b3b80d8