Continuing the work to add constraints to avoid invalid RTL
with autoinc addressing modes. Specifically this patch adds
the memory constraints similar to the pdp11.
gcc/
* config/h8300/constraints.md (Za..Zh): New constraints for
autoinc addresses using a specific register.
* config/h8300/h8300.cc (pre_incdec_with_reg): New function.
* config/h8300/h8300-protos.h (pre_incdec_with_reg): Add prototype.