Mingw keyword "interface" conflict in QtDBus

Short summary:
There is a build failure in QtDBus 5.6-alpha due to the usage of the preserved keyword "interface". build.log is attached.

Long summary:
The latest QtDBus changes in branch 5.6 have disclosed a very old problem. There are a lot public API methods in QDBusConnection which have the following argument:

const QString &interface

and there is also the method

QDBusConnectionInterface *QDBusConnection ::interface() const;

According to MSDN interface is a Windows C++ extension and a reserved keyword.

I can only speak for MinGW-w64 for now, but they indeed declare it in
i686-w64-mingw32\include\rpc.h

#ifndef _OBJC_
#undef interface
#define interface struct
#endif

Maybe due to some rearranges of header includes, this header is now included and causes the build failures in the attached build.log.

I did not yet submit any patch to gerrit, because there are several options how to address the issue. Attached is a easy fix from Fedora from 2013.