gdb: Add --with-python-libdir to gdb's --configuration output
    
    Commit:
    
      commit d13c7322fe1266984024644154003a19664610ea
      Date:   Fri Jan 17 00:10:22 2020 +0000
    
          gdb: Allow more control over where to find python libraries
    
    Added a new configuration option --with-python-libdir, but failed to
    add this option to the output of 'gdb --configuration'.  This commit
    fixes this mistake.
    
    gdb/ChangeLog:
    
    	* top.c (print_gdb_configuration): Print --with-python-libdir
    	configuration value.