nargs := make([]string, 0, len(args)+len(extraArgs))
	for _, arg := range args {
		if !strings.HasPrefix(arg, "-O") {
			nargs = append(nargs, arg)
		}
	}

	// Force -O0 optimization and append extra arguments, but keep the
	// trailing "-" at the end.
	li := len(nargs) - 1
	last := nargs[li]
	nargs[li] = "-O0"
	nargs = append(nargs, extraArgs...)

func gcWaitOnMark(n uint32) {
	for {
		// Disable phase transitions.
		lock(&work.sweepWaiters.lock)
		nMarks := work.cycles.Load()
		if gcphase != _GCmark {
			// We've already completed this cycle's mark.
			nMarks++
		}
		if nMarks > n {
			// We're done.
			unlock(&work.sweepWaiters.lock)
			return
		}

		// Wait until sweep termination, mark, and mark