[clang] [clang][analyzer] Correct SMT Layer for _BitInt cases refutations (PR #143310)

[Donát Nagy via cfe-commits]

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

LGTM but wait for the opinion of @steakhal as well.

(By the way, after tweaking the testcase, did you check that it would still crash without the improvements of the commit?)

https://github.com/llvm/llvm-project/pull/143310