Windows: Qt Webkit does not build with Qt 5.6

In qtwebkit/tools/qmake/mkspecs/features/functions.prf the following code is present:

LIBS += /OPT:REF -l$$target

When building on Windows, the "/OPT:REF" will be converted to "\OPT:REF" (probably by the path separator conversion) and the linker will understand this as a file name rather than an option.

The error message is:

LINK : fatal error LNK1104: cannot open file '\OPT:REF.obj'.