in newlib or Cygwin.
(process_spawnattr): Use sigprocmask rather than _sigprocmask. Use
sigaction rather than _sigaction.
(process_file_actions_entry): Use dup2 rather than _dup2.
(do_posix_spawn): Use execvpe rather than _execvpe. Use waitpid
rather than _waitpid.
* configure.host: Disable new posix_spawn function for all
users of posix dir except Cygwin.
* libc/posix/Makefile.am: Add support for new posix_spawn function.
* libc/posix/Makefile.in: Regenerate.
* libc/posix/posix_spawn.c: New file.
* libc/include/spawn.h: Ditto.