[clang] [llvm] [analyzer] Fix _BitInt support & casting behavior for Z3 symbolic execution (PR #210525)

[Balázs Benics via cfe-commits]

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

LGTM at glance.
I didn't really review this deeply because it doesn't affect anything that is supported so I think we are in the clear.

https://github.com/llvm/llvm-project/pull/210525