* child_info.h (cygheap_exec_info::sigmask): Declare new field.
* cygheap.cc (init_cygheap::find_tls): Rename threadlist_ix -> ix.  Only take
one pass through thread list, looking for eligible threads to signal.  Set a
new param indicating that function has found a sigwait* mask.
* cygheap.h (init_cygheap::find_tls): Reflect new parameter.
* dcrt0.cc (parent_sigmask): New variable.
(child_info_spawn::handle_spawn): Save parent's signal mask here.
(dll_crt0_1): Restore parent's signal mask to tls sigmask as appropriate.  Call
sig_dispatch_pending to flush signal queue when we can finally do something
with signals.
* exceptions.cc (sigpacket::process): Avoid attempting to handle signals if we
haven't finished initializing.  Rely on the fact that find_tls will do mask
checking and don't do it again.  Delete ill-named 'dummy' variable.
* sigproc.cc (cygheap_exec_info::alloc): Save calling thread's signal mask in
new sigmask field.
(wait_sig): Try to debug when WFSO fails and DEBUGGING is defined.
* thread.cc (pthread::set_tls_self_pointer): Make this a true automatic method
rather than inexplicably relying on a thread parameter.
(pthread::thread_init_wrapper): Accommodate set_tls_self_pointer change to
non-static.  Initialize sigmask before setting tid or suffer signal races.
* ehread.h (pthread::set_tls_self_pointer): Make non-static, delete parameter.
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