[ChangeLog][General Improvements] Qt's buildsystem now detects whether
the compiler supports C++14 and experimental support for C++1z. If the
compiler supports it, then Qt is automatically compiled using that
support.
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This does not apply to user applications built using qmake: those are
still built with C++11 support only. To enable support for C++14 in your
application, add to your .pro file: CONFIG += c++14 (similarly for
C++1z).

Change-Id: Ib056b47dde3341ef9a52ffff13ef1f5d01c42596
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>