[CIR] Upstream Exceptions support

Overview

Upstream support for Exceptions in ClangIR.

Suggested minimal test case

```
throw;

throw "Division by zero condition!"

try { } catch (...) {}
```


Existing incubator tests
- clang/test/CIR/CodeGen/throw.cpp
- clang/test/CIR/CodeGen/try-crach.cpp
