qRgba has undefined behavior

The definition of qRgba is:

inline Q_DECL_CONSTEXPR QRgb qRgba(int r, int g, int b, int a)// set RGBA value

{ return ((a & 0xff) << 24) | ((r & 0xff) << 16) | ((g & 0xff) << 8) | (b & 0xff); }

Shifting the alpha value has undefined behavior, it needs to be converted to an unsigned int first.

This results in slow code with Visual C++, when VC++ is using SSE auto-vectorization.

(qRgb does the right thing, it's using an unsigned constant of 0xffu as alpha value.)