QtBase: require python, drop gdb
QtBase: require python, drop gdb

The embedded V8 tree requires python for build. Drop GDB in hopes of
allowing Qt5 to build nicely on Mer.

Leave the commented-out xlib module addition in place. It can not be
built with OpenGLES, ever since xlib integration code started to require
GLX-context. We're targeting EGL, which comes from GLESv2 build
requirement. Unfortunately EGL and GLX appear to be mutually exclusive.

bostik/qt5-specs,bostik/qt5-specs