[clang] [analyzer] Handle [[assume(cond)]] as __builtin_assume(cond) (PR #116462)

[Balazs Benics via cfe-commits]

steakhal wrote:

I wanted to come back with another example:
```c++
int ternary_in_assume(int a, int b) {
  [[assume(a > 10 ? b == 4 : b == 10)]];
  if (a > 20)
    return b + 100; // expecting 104
  if (a > 10)
    return b + 200; // expecting 204
  return b + 300; // expecting 310
}
```

Actually, neither gcc, clang, msvc, or icc optimizes the return paths to constants - even though I think they would be allowed to. https://compiler-explorer.com/z/1ajvcvG9h

I'd need to think about of the implications for us though. I think it should be safe to eval these subexpressions and do state splits if and only if none of those expressions have sideeffects. In that case, they wouldn't be emitted into the CFG, so they shouldn't be a problem.

https://github.com/llvm/llvm-project/pull/116462