The tslib plugin cannot be configured to be built from top-level makefile

The tslib plugin must be built by hand.

It's not enabled by default and cannot be configured to be built
with the rest of the plugins, from a top-level make execution.

As this is really annoying, embedded frameworks such as open-embedded [1] or
buildroot will have to resort to patching Qt in order to support this option.

Looks like Qt5 should have some --enable-tslib or --with-tslib option in its
configure script.

[1] http://patchwork.openembedded.org/patch/50589/