ModGC

tentative: remove evict workaround #408

Job	Run time
check (default, macos-latest)	7m 25s
check (default, ubuntu-latest)	7m 38s
check (mmtk, release, macos-latest)	7m 20s
check (mmtk, release, ubuntu-latest)	8m 15s
	30m 38s

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