Work around a gcc bug in devel/qt5-qdoc to fix build of devel/qtcreator on 9.3

Instead of using std::sort() use qSort() on FreeBSD 9.3.
This should fix the pkg-fallout of devel/qtcreator.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59391
[2] https://bugreports.qt.io/browse/QTBUG-43057

Reviewed by: rakuco
Approved by: rakuco (mentor)
Differential Revision: https://reviews.freebsd.org/D8121