LNK2019 error in the C++ interface

[dokutoku]

I tried to use a function from a library written in C++ in D. 
I've been trying to use it in D. But I got an error in LNK2019 
and the build failed.

So I created a simple static library as follows and built it.

```cpp
#pragma once

#include <windows.h>

namespace static_test {
	void str_test(LPCSTR str)
	{
		MessageBoxA(NULL, str, NULL, MB_OK);
	}

	void wstr_test(LPCWSTR str)
	{
		MessageBoxW(NULL, str, NULL, MB_OK);
	}

	void rect_test(RECT rect)
	{
	}
}
```

```d
import core.sys.windows.windows;
import std.utf;

extern (C++, "static_test") {
	nothrow @nogc
	extern void str_test(LPCSTR str1);

	nothrow @nogc
	extern void wstr_test(LPCWSTR str1);

	nothrow @nogc
	void rect_test(RECT rect);
}

void main()
{
	str_test(toUTFz!(const char*)("test"));

	// error LNK2019
	wstr_test(toUTF16z("test"w));

	// error LNK2019
	rect_test(RECT.init);
}
```

The LNK2019 error still occurred.
I'm guessing that the reason for the error is that the type 
declared in C++ is different from the type declared in D. But I'm 
not sure how to fix it.