Make QStringBuilder use memcpy for QByteArrayLiteral

There is no need to do a bytewise copy looking for the terminating
nul-character when the size of the data is statically declared and known
ahead of time.

Change-Id: I787745a58955d1a366624f9ea92e9e701de8c981
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstringbuilder.h

@@ -376,9 +376,8 @@ template <int N> struct QConcatenable<QStaticByteArrayDataPtr<N> > : private QAb
 #endif
     static inline void appendTo(const type &ba, char *&out)
     {
-        const char *a = ba.ptr->data;
-        while (*a)
-            *out++ = *a++;
+        ::memcpy(out, ba.ptr->data, N);
+        out += N;
     }
 };