* sysdeps/mach/hurd/setitimer.c: Code rearranged a bit to use new
preemption interface.
* sysdeps/mach/hurd/i386/trampoline.c (_hurd_setup_sighandler):
Use _hurdsig_catch_memory_fault.
* hurd/Makefile (headers): Add hurd/sigpreempt.h.
(sig): Add catch-signal.
* hurd/hurdfault.c (_hurdsig_fault_catch_exception_raise):
Rewritten using a preempter in new interface.
* hurd/hurdfault.h (_hurdsig_catch_fault): Likewise.
(_hurdsig_catch_memory_fault): New macro.
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