Handle unions in header-translator #3314

Job	Run time
Check formatting	11s
Check MSRV	56s
Lint macOS x86_64	3m 25s
Lint iOS ARMv7s	3m 24s
Lint visionOS Aarch64 simulator	3m 16s
Lint GNUStep + exceptions	1m 27s
Lint header-translator	28s
Lint test-assembly	1m 7s
Test macOS 15 Aarch64	1m 25s
Verify header translator output	1m 52s
Assembly tests	51s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Check framework features	0s
Test Compiler-RT	32s
Test GNUStep with libobjc2 v1.9	1m 14s
Compiler UI	47s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.0	1m 20s
Test GNUStep with libobjc2 v2.1 on nightly	1m 3s
Test GNUStep 32bit	1m 23s
	24m 41s

Provide feedback