Fix the shift patterns, and add test

Firstly, it adds back the split conditions that I accidentally removed.
Without it the dot insns are never generated, or rather, always split
back to a separate compare instruction.

Secondly, the shift amount should be SI always, not GPR, or GCC will
insert a zero-extend at expand time that it cannot get rid of later.

The test tests whether dot-form instructions are generated for both
"dot" and "dot2" cases, that is, with just a CC output or also a GPR
output; for all four basic shifts, with a register amount or an
immediate amount.  It also tests for superfluous zero-extends.  This
also tests if combine "simplifies" the rotates to right-rotates, which
it shouldn't do anymore.

From-SVN: r212267