qt5: Need pcre with UTF support

Enabling PCRE16 is not enough for Qt5. PCREUTF is also necessary, else
Qt5 may complain with this kind of (non fatal) message:
  QRegularExpressionPrivate::doMatch(): called on an invalid QRegularExpression object

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>