makejob
jp = makejob(NULL, 1);
jp = makejob(cmd, 1);
forkshell(jp = makejob(n, 1), n, backgnd?FORK_BG:FORK_FG) == 0) {
jp = makejob(n, pipelen);
jp = makejob(n, 0); /* 0 --> leave jobs_invalid, no jobctl */
struct job *makejob(union node *, int);