Special-case IMP when translating headers #3135

Job	Run time
Check formatting	13s
Check MSRV	48s
Lint macOS x86_64	2m 28s
Lint iOS ARMv7s	2m 21s
Lint visionOS Aarch64 simulator	2m 20s
Lint GNUStep + exceptions	1m 21s
Lint header-translator	1m 10s
Lint test-assembly	30s
Test macOS 15 Aarch64	1m 35s
Verify header translator output	53s
Compiler UI	48s
Assembly tests	57s
Check framework features	0s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test Compiler-RT	23s
Test GNUStep with libobjc2 v1.9	57s
Test GNUStep with libobjc2 v2.0	1m 26s
Test GNUStep with libobjc2 v2.1 on nightly	1m 3s
Test on iOS simulator w. dinghy	0s
Test GNUStep 32bit	1m 19s
	20m 32s

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