intr: add interrupt FOREACH macro

[ehem_freebsd_m5p.com]

Summary

Another thing sometimes needed, looping over all interrupts. This
iterates over all allocated interrupt numbers.

[ehem_freebsd_m5p.com]

Hmm, then I spot the error...

[ehem_freebsd_m5p.com]

Ick, dropping the idea of a common maximum possible interrupt number variable. Had seemed worthwhile, but now I'm unsure.

[ehem_freebsd_m5p.com]

While at it, appears Herald rule H67 has been broken by the configuration change for arc (defaults to rG, not rS).

[ehem_freebsd_m5p.com]

Naturally finding bugs during full build...

[ehem_freebsd_m5p.com]

This doesn't do much more than provide some support for D36610. I'm unsure of the approach, but needed something to maintain compatibility with D36610. I won't be surprised by abandoning this if a better approach is suggested.

[ehem_freebsd_m5p.com]

The need would be addressed by D37870. Since that is simpler and likely less controversial, go with that.