Building WebKit in Qt 5.6 Makefile generation creates \OPT:REF instead of /OPT:REF

I know that WebKit is removed from the package, but its still supposed to build from source. which is no longer the case

a number of the generated Makefiles have incorrect reference to OPT:REF
its been generated as \OPT:REF which the linker is assuming is an obj file when in fact its supposed to be /OPT:REF linker option.

manually editing the Makefiles with the bad option allows one to proceed, but it should work out of git.

doing a shadow build configure of Qt with WebKit from git

not the only person who has seen this.

http://stackoverflow.com/questions/33631235/building-qtwebkit-with-qt-5-6-on-windows

qtwebkit/Source/Makefile.api.Debug
qtwebkit/Source/Makefile.api.Release
qtwebkit/Source/JavaScriptCore/Makefile.jsc.Debug
qtwebkit/Source/JavaScriptCore/Makefile.jsc.Release