[Development] DEFAULT_INCDIR and DEFAULT_LIBDIR in Qt 5.8/configure

[René J. V. Bertin]

Thiago Macieira wrote:

> Also, the Xcode's clang doesn't search /usr/local/include when the --sysroot
> option is passed. It's possible we performed an incorrect detection in Qt 5.7
> and earlier, but the 5.8 detection should be better.

Sorry, I didn't make this explicit, but I only had to prune on Linux (I use 
almost the same build scripts on both platforms, Mac and Linux). It didn't seem 
completely relevant for the original question (where the code had gone).

I don't think the reason why I ever needed the pruning is of much general 
interest anyway. We'll see if/when the need manifests itself again.

R.