gdb: include readline in default PACKAGECONFIG
gdb: include readline in default PACKAGECONFIG

* without readline in PACKAGECONFIG and with no-static-libraries.inc
  gdb fails when trying to build against own bundled static readline

Signed-off-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@gmail.com>

kraj/meta-qt5,kraj/meta-qt5,meta-qt5/meta-qt5,opendreambox/meta-qt5,sapiippo/meta-qt5,timopulkkinen/meta-qt5,sapiippo/meta-qt5,schnitzeltony/meta-qt5,opendreambox/meta-qt5,timopulkkinen/meta-qt5,schnitzeltony/meta-qt5,opendreambox/meta-qt5,meta-qt5/meta-qt5,timopulkkinen/meta-qt5,timopulkkinen/meta-qt5