re PR bootstrap/14316 (collect2 doesnt build on windows hosts)

	PR bootstrap/14316
	* collect2.c: Never include <vfork.h>.
	(VFORK_STRING, vfork): Don't define.
	(pid): Remove global variable.
	(handler): Call raise instead of kill (getpid(), ...).
	(collect_wait): Add pex parameter.  Change all callers.  Use
	pex_get_status rather than pwait.
	(do_wait): Add pex parameter.  Change all callers.
	(collect_execute): Return struct pex_obj * rather than void.  Use
	pex routines rather than pexecute.
	(fork_execute): Get pex_obj from collect_execute, and pass it to
	do_wait.
	(scan_prog_file): Use pex routines rather than pipe/vfork/exec.
	Only declare quit_handler if SIGQUIT is defined.
	(scan_libraries): Likewise.
	* collect2.h (collect_execute): Update declaration.
	(collect_wait): Update declaration.
	* tlink.c (tlink_execute): Get pex_obj from collect_execute, and
	pass it to collect_wait.

From-SVN: r97199