[patch][gold] Use LIFO instead of FIFO to implement gc's transitive closure

[Rafael Espíndola]

> Minor nitpick: Posting numbers with ten decimal places without any
> indication of the standard deviation is not very informative.

Fair enough. I was just lazy and copy and pasted the number out of perf.

I did a new run this morning. The full logs are attached.

Cheers,
Rafael
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