[Bug 47710] New: objidl.h contains invalid C++

https://bugs.winehq.org/show_bug.cgi?id=47710

Bug ID: 47710
           Summary: objidl.h contains invalid C++
           Product: Wine
           Version: 4.15
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: winelib
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Hello,

as of wine 4.15, building a winelib version of DXVK fails with the following
error:

/usr/include/wine/windows/objidl.h:6100:15: error: ‘union
_userSTGMEDIUM::<unnamed struct>::__WIDL_objidl_generated_name_0000000C’
invalid; an anonymous struct may only have public non-static data members
[-fpermissive]
 6100 |         union __WIDL_objidl_generated_name_0000000C {
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The problem is that C++ does not allow declaring named unions or structs inside
anonymous structs since it treats this as a nested type. Moreover, the
anonymous struct that it is defined in seems unnecessary, although I might be
missing some detail there.

Defining __WIDL_objidl_generated_name_0000000C as an empty string before
including windows.h works around this problem.