This makes the difference between selector matching scaling on the ARM
Cortex-A9 and not, because the auto-derived `PartialEq` implementation
blows out the 32KB I-cache. With this change, there is a 2x improvement
in selector matching over sequential when using all 8 cores. (More work
needs to be done; this is a start.)
r? any DOM expert
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c3d242544e
