See the post by Allan Sandfeld Jensen 17 Apr 2013 16:05
The patch disabling this didn't make it for Qt 5.0.2, so please
note that Qt 5.0.2 will currently not work out of the box on older x86
processors without SSE2. In Qt 5.1.0 and QtWebKit 2.3.2 I expect to include a
proper patch for LLInt without SSE2.
Qt 5.1.0 and QtWebKit 2.3.2 may offer a solution?