* configure.in: Call AC_FUNC_VFORK.
* collect2.c: Define VFORK_STRING as a printable string for
error messages (either "vfork" or "fork".) If HAVE_VFORK_H is
defined, include vfork.h. If VMS is defined, define vfork()
appropriately. Remove vfork check on USG, we're using autoconf.
(collect_execute): Pass VFORK_STRING to fatal_perror instead of
checking locally what string to pass.
(scan_prog_file): Likewise.
(scan_libraries): Likewise.
* gcc.c: Remove vfork check on USG, we're using autoconf.
Besides, no calls to vfork/fork occur in this file.
* protoize.c: Likewise.