(prepare_scc_operands): Force sh_compare_op1 to a register if
it is an invalid constant.
(output_branch): Add cases for 4, 8, and 18.  Correct branch offsets
in comments.
(find_barrier): Correct test for move instructions that need to be
fixed by verifying that the set source is a bad constant.
(arith_reg_or_0_operand): New function.

From-SVN: r8824