Improved linker-debugger interface

[Tom Tromey]

Paul> Once the probe is located, the in-process debugger still has a problem:
Paul> not enough space to place a patch on (in-process debugger can not put a
Paul> breakpoint on the one instruction that is available).

Paul> Making the probes wider would be ideal.

I asked and the SystemTap guys said that they'd welcome a patch, but
that the widening would have to be optional.  (There are already a
couple of knobs in sdt.h, controlled by some #define.)

Tom