Use `extern "C-unwind"` #3019

Job	Run time
Check MSRV	50s
Check formatting	11s
Lint macOS 64bit	2m 44s
Lint iOS 32bit	2m 1s
Lint GNUStep + exceptions	1m 26s
Lint header-translator	28s
Lint test-assembly	25s
Test macOS 12	2m 43s
Verify header translator output	49s
Assembly tests	3m 22s
Test macOS 13	4m 5s
Check framework features	10m 31s
Test macOS 14	1m 54s
Test Compiler-RT	28s
Build macOS AArch64	1m 52s
Test GNUStep with libobjc2 v1.9	38s
Test macOS old SDK	5m 37s
Test on iOS simulator w. dinghy	10m 33s
Test GNUStep with libobjc2 v2.0	42s
Test macOS nightly	2m 15s
Compiler UI	1m 44s
Test GNUStep with libobjc2 v2.1 on nightly	45s
Build macOS 32bit	9m 16s
Test GNUStep 32bit	1m 12s
Build iOS simulator ARM64	1m 38s
Build iOS ARM64	1m 35s
Build iOS ARMv7s	2m 26s
Build iOS 32bit x86	2m 23s
	1h 14m 33s

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