Improve fix: #20867 ICE on final switch forward referencing its enum.

[abulgit]

Fix: #21094
Improve the PR: #21001 (Fix: Prevent ICE on final switch forward referencing its enum)
I set ed.semanticRun = PASS.semantic2done at the end of the C enum processing

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[dkorpel]

Cool, can you add a test case in test/compilable?