WinRT: Added msvc2013 mkspecs

Change-Id: I052f6ba19056e7c0df6d7ea5548eb4dac4db125e
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
qmake: Support MSVC2013 for WinRT builds

Change-Id: I1c102f0b029616997d72933a90c0f9a2a3a9e222
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Clean up common winrt/winphone mkspec

Change-Id: I010bf977e01fab2f39184bbe730ec70128cc2982
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>