Introduce MODULAR_GC_FN #618

Job	Run time
omnibus compilations, trigger	2s
omnibus compilations, #2	32m 40s
omnibus compilations, #1	27m 35s
omnibus compilations, #3	30m 19s
omnibus compilations, #4	25m 8s
omnibus compilations, #11	26m 26s
omnibus compilations, #9	26m 48s
omnibus compilations, #12	23m 34s
omnibus compilations, #5	26m 38s
omnibus compilations, #7	32m 30s
omnibus compilations, #8	26m 41s
omnibus compilations, #6	27m 8s
omnibus compilations, #10	26m 21s
omnibus compilations, result	3s
	5h 31m 53s

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