* dcrt0.cc (dll_crt0_1): Move set_os_type.

* dcrt0.cc (dll_crt0_1): Move set_os_type.
(_dll_crt0): To here.
(cygwin_dll_init): And here.
* external.cc (fillout_pinfo): Use more foolproof method for scanning for pids.
* pinfo.cc (set_myself): Eliminate myself_identity.init.
* sigproc.cc (wait_sig): Do it here instead to reduce the amount of time where
there could potentially be two processes with the same pid.
* spawn.cc (spawn_guts): Eliminate duplicate initialization.
* include/sys/cygwin.h: Mark unused PID_* elements.