gdb: more infrun debug from breakpoint.c

gdb: more infrun debug from breakpoint.c

This commit adds additional infrun debug from the breakpoint.c file.
The new debug output all relates to breakpoint condition evaluation.

There is already some infrun debug emitted from the breakpoint.c file,
so hopefully, adding more will not be contentious.  I think the
functions being instrumented make sense as part of the infrun process,
the inferior stops, evaluates the condition, and then either stops or
continues.  This new debug gives more insight into that process.

I had to make the bp_location* argument to find_loc_num_by_location
const, and add a declaration for find_loc_num_by_location.

There should be no user visible changes unless they turn on debug
output.