set prototyped hdr vfork sys vfork tst run{ if test "$_hdr_vfork" = 1 then echo "#include <vfork.h>" elif test "$_sys_vfork" = 1 then echo "#include <sys/vfork.h>" else echo '#include <unistd.h>' > $tmp.c $cc -E $tmp.c | grep vfork fi }end