qt5script: Check for QtGui before building the examples

qt5script: Check for QtGui before building the examples

Adding an upstream patch to fix an autobuild failure.

qsdbg and marshal examples need QtGui module. If QtGui is not installed
they fail to compile.

Upstream commit:
   https://github.com/qtproject/qtscript/commit/e4453c92ee41943a3a1d67a725804a44e747f64e

Fixes:
   http://autobuild.buildroot.net/results/0e6/0e63bc604f3ec422996eb0f5fd92f4437954ca04/

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>