Do generic rs_machine_dependent relaxation only if TC_GENERIC_RELAX_TABLE is
defined. Use its value as the base of the table, so the actual declaration
can be cpu-specific (and const or not as appropriate). For other cpus where
this isn't done (the majority), delete md_relax_table altogether.
For machines with WORKING_DOT_WORD, delete md_{short,long}_jump_size.