[InstCombine][X86] Tweak generic expansion of PACKSS/PACKUS to shuffle then truncate. NFCI.

This has no effect on constant folding but will be useful when we expand non-saturating PACKSS/PACKUS intrinsics.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@359191 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed