Patch: add systemtap-style marker to _Unwind_DebugHook

[Tom Tromey]

Roland> That test would work.  (That macro is not defined at all in
Roland> earlier versions.)

Tom> Here is an updated version.

Tom> 2011-01-14  Tom Tromey  <tromey@redhat.com>
Tom> 	* unwind-dw2.c: Include sys/sdt.h if it exists.
Tom> 	(_Unwind_DebugHook): Use STAP_PROBE2.
Tom> 	* config.in, configure: Rebuild.
Tom> 	* configure.ac: Check for sys/sdt.h.

Now that Stage 1 is open, I am checking this in.

Tom