[Development] MSVC 2017 15.8 upgrade

[Thiago Macieira]

If you upgraded MSVC 2017 to 15.8 yesterday and you try to build qtbase, 
you'll get a build error. This is fixed, but you need to make sure you erase 
.qmake.stash files everywhere, since they contain the cached version of the 
compiler.

And since neither nmake nor jom update Makefiles on their own, erase them all 
too.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center