Ivana Ivanovska ce2ff0a35d Add support for int return type in Carbon/C++ interop (#5114) ...

Adding support for importing C++ functions with `int` return type in
Carbon.

Part of #5063

Here is a demo of the functionality:

```c++
// hello_int.h;

auto foo_int() -> int;
```

```c++
// hello_int.cpp

#include "hello_int.h"

auto foo_int() -> int {
    return 1;
}
```

```carbon
// main.carbon

library "Main";

import Cpp library "hello_int.h";
import Core library "io";

fn Carbon_foo(b: i32) {
  Core.Print(b);
}

fn Run() -> i32 {
  Carbon_foo(Cpp.foo_int());
  return 0;
}
```

```
$ clang -c hello_int.cpp
$ bazel-bin/toolchain/carbon compile main.carbon
$  bazel-bin/toolchain/carbon link hello_int.o main.o --output=demo
$ ./demo
1
```

2025-03-24 15:18:20 +00:00

..

no_prelude

Add support for int return type in Carbon/C++ interop (#5114)

2025-03-24 15:18:20 +00:00

function_decl.carbon

Add support for int return type in Carbon/C++ interop (#5114)

2025-03-24 15:18:20 +00:00