[clang] [clang][StaticAnalysis] Fix an false negative bug in handling '__builtin*overflow' (PR #214553)

[Balázs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

LGTM given that you reword the test comment such that it reflects the current state of reasoning: There is no FN, there is no "should".

https://github.com/llvm/llvm-project/pull/214553