This makes it symmetric with the 'u' modifier that forces an unsigned type.
This is needed for unsigned vector shifts, where the shift amount still needs
to be signed. PR8482 (Radar 8603521).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119742 91177308-0d34-0410-b5e6-96231b3b80d8
