Improved linker-debugger interface

[Tom Tromey]

Tom> Right now a SystemTap probe is a single nop, so probably no joy there.
Tom> We have talked about making it a wider nop, though, to facilitate this
Tom> kind of patching, primarily I think by LTTng.  What do you think of
Tom> this?

Oh, and if it won't work, or if you need something extra, now is the
best time to write up your requirements for Gary's consideration.

Tom