when printing the GDB config, explicitly say if configured without python

when printing the GDB config, explicitly say if configured without python

When using the --configuration command line switch, or using
the "show configuration" command with a version of GDB which
was configured without Python supoprt, this patch changes
the resulting output to include...

    --without-python

... instead of not printing anything about Python support.

gdb/ChangeLog:

        * top.c (print_gdb_configuration): Print "--without-python"
        if GDB was configured without Python.

Tested on x86_64-linux by rebuilding GDB with and without Python,
and checking the output of "gdb --configuration" in both cases.