[Interest] Can't build Qt 5.4.2 properly on virtual systems

[Rutledge Shawn]

I think qttools has a dependency on webkit, because if I configure with -no-icu, or if I am doing an Android build, then qttools never gets built automatically, and I have to do it manually.  (It would be the same if some of webkit’s extra dependencies are not in place.)  The reason is that assistant does a better job of rendering help if it can use webkit, but it’s not a hard dependency.  So I think it would be nice if we could make the build continue with or without webkit.  But it’s also not that much trouble to build one more module by hand, if you have checked out the repo successfully.