Refurbish add compare patterns: use 'r' constraint, fix identation,
and fix pattern to match 'if (a+b) { ... }' constructions.
gcc/
* config/arc/arc.cc (arc_select_cc_mode): Match NEG code with
the first operand.
* config/arc/arc.md (addsi_compare): Make pattern canonical.
(addsi_compare_2): Fix identation, constraint letters.
(addsi_compare_3): Likewise.