Wrong constructor on MSVC (default constructor closure)

To confirm, it looks like that extra constructor case is the "default
constructor closure," which is generated when dllexporting a default
constructor that requires some extra code to call, and the
clang_Cursor_getCXXManglings solution handles it incorrectly.

For example, this code generates two constructors, with symbols
??0Foo@@QEAA@H@Z (public: __cdecl Foo::Foo(int)) and ??_FFoo@@QEAAXXZ
(public: void __cdecl Foo::\default constructor closure'(void)`).

struct __declspec(dllexport) Foo {
    Foo(int x = 3);
};

Bindgen declares the first but gives it the link_name of the second:

extern "C" {
    #[link_name = "??_FFoo@@QEAAXXZ"]
    pub fn Foo_Foo(this: *mut Foo, x: ::std::os::raw::c_int);
}

Reproduce the reported MSVC case using the shown dllexported C++ Foo with a default argument, then inspect how clang_Cursor_getCXXManglings is used for constructor declarations. Compare the generated Foo_Foo declaration with the two symbols described in the issue; done means the declared constructor is linked to the actual constructor symbol rather than the default constructor closure.