* assert.cc (__assert): Call debugger on assertion failure if debugging.

* assert.cc (__assert): Call debugger on assertion failure if debugging.
* dcrt0.cc (dll_crt0_1): Just wait for signal thread to go live rather than
going through the overhead of invoking it.
* fork.cc (fork_child): Ditto.
* exceptions.cc (signal_fixup_after_fork): Call sigproc_init here.
* sigproc.cc (proc_can_be_signalled): Assume that the signal thread is live.
(sig_dispatch): Ditto.
(sig_send): Ditto.
(wait_for_sigthread): Renamed from "wait_for_me".  Assume that wait_sig_inited
has been set and that this function is only called from the main thread.
* winsup.h (wait_for_sigthread): Declare new function.