If the compiler supports C++11 alignof, let's use it. No point in
perpetuating the use of __alignof__ or __alignof.
There's a fallback implementation in qglobal.h that works even without
compiler extensions. We can't drop it just yet (alignas is not a
required C++11 feature), but at this point I doubt that fallback is used
anywhere anymore.
The tst_compiler test was wrong to use alignof(variable). That's not
permitted by the standard nor would it work with our fallback
implementation. MSVC 2015 enforces this, but ICC, GCC and Clang don't.
Change-Id: Ifea6e497f11a461db432ffff1448abfa86672c63
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
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