[clang] [CIR] Implement Statement Expressions (PR #153677)

[Morris Hafner via cfe-commits]

================
@@ -0,0 +1,166 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
----------------
mmha wrote:

`stmtexpr-init.c` is not useful because we lack record init list exprs. I added a few C++ tests but I noticed that we don't call destructors for prvalues:

```c++
struct with_dtor {
  ~with_dtor();
};

void cleanup() {
  with_dtor{};
}
```

So I didn't cover those in the statement expr tests, yet.

https://github.com/llvm/llvm-project/pull/153677