ModGC

reorder gen_guard_type, more specific go first #2663

Job	Run time
check (default, macos-latest)	8m 25s
check (default, ubuntu-latest)	7m 19s
check (mmtk, release, macos-latest)	11m 17s
check (mmtk, release, ubuntu-latest)	11m 17s
	38m 18s

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