The option /DEBUG:FASTLINK has been introduced in Visual Studio 2015.
However, qmake sometimes activates this option for older versions of Visual Studio (2013 in my case).
This bug generates build errors in Visual Studio.
After a quick search in the qmake code, I found the use of a uninitialized member (DebugInfoOption) in qtbase/qmake/generators/win32/msvc_objectmodel.cpp.
I have attached a patch containing a quick fix for this bug.