fix(@angular/build): handle postcss compilation errors gracefully #694

Job	Run time
list	39s
workflow (build-cli)	2m 7s
workflow (modules-builder-tests)	2m 32s
workflow (devkit-core-tests)	1m 55s
workflow (devkit-core-tests-rerun)	2m 5s
workflow (build-unit-tests)	3m 47s
	13m 5s

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