cgen: fix codegen for if comptime with `-g` #7993

Job	Run time
tests-sanitize-address-clang	2h 9m 31s
tests-sanitize-address-gcc	2h 39m 11s
tests-sanitize-address-msvc	4m 11s
tests-sanitize-memory-clang	3h 26m 46s
tests-sanitize-undefined-clang	1h 2m 43s
tests-sanitize-undefined-gcc	1h 38m 27s
	11h 0m 49s

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