build

Compiler: only flush the necessary env for closure #2415

Job	Run time
lint-fmt	3m 39s
build (ubuntu-latest, 4.08.x, true, true, true)	8m 19s
build (ubuntu-latest, 4.09.x, true, true, true)	6m 15s
build (ubuntu-latest, 4.10.x, true, true, true)	5m 4s
build (ubuntu-latest, 4.11.x, true, true, true)	8m 6s
build (ubuntu-latest, 4.12.x, true, true, true)	6m 15s
build (ubuntu-latest, 4.13.x, true, true, true)	7m 51s
build (ubuntu-latest, 5.0.x, true, true, true)	6m 28s
build (ubuntu-latest, 4.14.x, true, false, true)	10m 25s
build (macos-latest, 4.14.x, true, false, true)	26m 34s
build (windows-latest, 4.14.x, true, false, true)	30m 57s
build (ubuntu-latest, 5.1.x, false, false, false)	15m 13s
build (macos-latest, 5.1.x, true, false, true)	25m 22s
build (windows-latest, ocaml.5.1.1,ocaml-option-mingw, false, false, true)	32m 4s
	3h 12m 32s

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