Eliminate use of sigframe and sigthread throughout.

Eliminate use of sigframe and sigthread throughout.
* Makefile.in (DLL_OFILES): Add sigfe.o.  Remove reliance on cygwin.def from
cygwin0.dll dependency since dependence on sigfe.o implies that.  Generate def
file on the fly using 'gendef'.
* configure.in: Don't auto-generate cygwin.def.
* configure: Regenerate.
* cygwin.din: Add SIGFE stuff where appropriate.
* dcrt0.cc (dll_crt0_1): Initialize cygwin tls early in process startup.  Set
_main_tls to address of the main thread's cygwin tls.
* debug.h: Remove now unneeded WFSO and WFMO declarations.
* exceptions.cc (_last_thread): Define.
(set_thread_state_for_signals): New function.
(reset_thread_exception_for_signals): Ditto.
(init_thread_for_signals): Ditto.
(delete_thread_for_signals): Ditto.
(capture_thread_for_signals): Ditto.
(handle_exceptions): Set return address explicitly for exceptions prior to
calling sig_send.
(interrupt_on_return): Eliminate.
(setup_handler): Add preliminary implementation for dealing with
thread-specific signals by querying _main_tls.
(signal_exit): Use cygthread::main_thread_id instead of mainthread.id.
(call_signal_handler_now): For now, just handle the main thread.
* fork.cc (vfork): Save and restore main _my_tls.
* gendef: New file.  Generates def file and sigfe.s file.
* gentls_offsets: New file.  Generates offsets for perl to use in sigfe.s.
* how-signals-work.txt: Mention that info is obsolete.
* init.cc (dll_entry): Initialize cygwin tls storage here.
* miscfuncs.cc (low_priority_sleep): Make a C function for easier calling from
asm.
* perthread.h (vfork_save::tls): New element.
* signal.cc (nanosleep): Replace previous use of
sigframe.call_signal_handler_now with straight call to call_signal_handler_now.
(abort): Ditto.
* syscalls.cc (readv): Ditto.
* termios.cc (tcsetattr): Ditto.
* wait.cc (wait4): Ditto.
* sigproc.cc (sig_dispatch_pending): Ditto.
(sig_send): Ditto.
* sigproc.h: Declare call_signal_handler_now.
* thread.cc (pthread::thread_init_wrapper): Initialize cygwin tls.  Remove
obsolete and unworking signal stuff.
* thread.h (verifyable_object::sigs): Eliminate.
(verifyable_object::sigmask): Eliminate.
(verifyable_object::sigtodo): Eliminate.
(verifyable_object::exit): Make attribute noreturn.
(verifyable_object::thread_init_wrapper): Ditto.
(pthread_null::exit): Ditto.
* winbase.h (__stackbase): Always define.
* winsup.h (low_priority_sleep): Declare as a "C" function.
* include/cygwin/version.h: Bump API version to reflect sigwait export.
* include/sys/queue.h: Protect SLIST_ENTRY from previous declaration.
* signal.cc (sigwait): Implement.
* select.cc (fhandler_base::ready_for_read): Add debugging output.
* devices.h: Define more device pointers via their storage.
* devices.in: Don't parse things like /dev/inet/tcp, as they really have no
meaning.
* devices.cc: Regenerate.
* gendevices: Set proper protection for output file.
* cygtls.h: New file.
* gendef: New file.
* gentls_offsets: New file.
* tlsoffsets.h: New file.  Autogenerated.
* config/i386/longjmp.c: Remove.  File subsumed by gendef output.
* config/i386/makefrag: Remove obsolete file.
* fhandler.cc: Remove spurious access_worker declaration.
* spawn.cc (spawnve): Make debugging output more accurate.
* cygwin-gperf: Remove.
* devices.cc: Remove.