[SystemZ] Prefer comparisons with zero

Convert >= 1 to > 0, etc.  Using comparison with zero isn't a win on its own,
but it exposes more opportunities for CC reuse (the next patch).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187571 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Reuse CC results for integer comparisons with zero

This also fixes a bug in the predication of LR to LOCR: I'd forgotten
that with these in-place instruction builds, the implicit operands need
to be added manually.  I think this was latent until now, but is tested
by int-cmp-45.c.  It also adds a CC valid mask to STOC, again tested by
int-cmp-45.c.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187573 91177308-0d34-0410-b5e6-96231b3b80d8