[CIR] Upstream support for constructing globals

### Overview
Upstream support for calling constructors when C++ struct/class variables are declared as globals.

### Suggested minimal test case
```
struct S {
  S();
};
S s;
```

### Existing incubator tests
clang/test/CIR/CodeGen/global-new.cpp
clang/test/CIR/CodeGen/struct.cpp