[clang] [clang][StaticAnalyzer] Adding getentropy to CStringChecker. (PR #83675)

[via cfe-commits]

https://github.com/NagyDonat requested changes to this pull request.

I'll try to take over this review process and help with finalizing this commit. I also added @balazske who's also familiar with this area.

Unfortunately currently there are significant problems in the state/assumption manipulation logic: it looks as if you thought that functions like `assumeZero` and `assume` always returned one nullpointer and one non-null state ref (in either order) -- while they have a third possibility where both returned references are non-null.

https://github.com/llvm/llvm-project/pull/83675