NFC Factor out common code between updateGOT and reportUndefinedSymbols

[hoodmane]

Suggested in discussion on #22053

[hoodmane]

@sbc100 I think the failure is a flake.

[kripken]

I re-ran tests here but the error recurred, though it did look like a flake. I tried to update the branch to fix that but now more tests fail, so there may be a larger issue here.