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

[Balazs Benics via cfe-commits]

steakhal wrote:

So we had the following assertion failure:
```
clang/lib/Analysis/ThreadSafety.cpp:529: LocalVariableMap::addDefinition: Assertion `!Ctx.contains(D)' failed.
```
On `libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/pstl.fill_n.pass.cpp`.

I wish I could come back to this to see why that assert fails. I don't have the bandwidth. Maybe at some point in January.

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