fix(@angular/build): emit a warning when `outputHashing` is set to `a… #1442

Job	Run time
list	25s
workflow (modules-builder-tests)	1m 39s
workflow (devkit-core-tests-rerun)	1m 13s
workflow (devkit-core-tests)	1m 9s
workflow (build-unit-tests)	2m 6s
workflow (build-cli)	1m 37s
	8m 9s

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