* exceptions.cc (setup_handler): Avoid suspending a thread if it in a cygwin

* exceptions.cc (setup_handler): Avoid suspending a thread if it in a cygwin
function, in an exception, spinning, or locked.
* gendef (_sigfe): Move incyg setting earlier.
(sigreturn): Set incyg flag to avoid interrupting called cygwin functions.
(sigdelayed): Ditto.
(stabilize_sig_stack): Ditto.
* sigproc.cc (proc_subproc): Don't restore process lock early in exec case.
* cygtls.h: Reorganize fields in _cygtls slightly.
* tlsoffsets.h: Regenerate.