*_ALIGN_MAX_SKIP macros

[DJ Delorie]

 JUMP_ALIGN_MAX_SKIP
 LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
 LOOP_ALIGN_MAX_SKIP
 LABEL_ALIGN_MAX_SKIP

None of these macros take any parameters, but for optimal performance
on RX, it's key to match the max_skip with the size of the following
opcode - there's a penalty only if you branch to an opcode which spans
fetch groups, but it's the same penalty as running a NOP opcode, so
you don't want to add nops if you don't have to.

Can we extend those macros to take the label as a parameter?  From
that, the backend could find the next actual insn.