Including math.h can pollute the default namespace, and break
some compilers if cmath versions of the method are declared as using.
Switching to C++ math functions also greatly simplifies handling of
float qreal as C++ automatically chooses the right method.
[ChangeLog][QtCore][QtMath] qmath.h no longer includes math.h, so any
sources depending on that indirect inclusion may fail to build.
Change-Id: I4d0e331dafba354ec05dc5052e61ef4ff8d387fe
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
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