Add more warnings to crate root #2129

Job	Run time
Check MSRV	1m 38s
Check formatting	9s
Lint macOS 64bit	5m 47s
Lint iOS 32bit	1m 21s
Lint GNUStep + exceptions	2m 6s
Lint header-translator	33s
Lint test-assembly	38s
Test macOS 12	6m 46s
Verify header translator output	1m 11s
Assembly tests	1m 4s
Test Compiler-RT	39s
${{ matrix.name }}	0s
Check icrate features	0s
Test GNUStep with libobjc2 v1.9	4m 54s
Test GNUStep with libobjc2 v2.0	4m 30s
Test GNUStep with libobjc2 v2.1 on nightly	5m 0s
Test GNUStep 32bit	4m 5s
Compiler UI	1m 2s
Test on iOS simulator w. dinghy	0s
	41m 23s

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