Fix compilation warnings triggered by Python's pyerrors.h

[Eli Zaretskii]

> Date: Tue, 19 Mar 2013 14:13:56 -0700
> From: Joel Brobecker <brobecker@adacore.com>
> Cc: tromey@redhat.com, gdb-patches@sourceware.org
> 
> > It worked, so I committed the below.
> > 
> > Could someone please do me a favor and commit the same to the 7.6
> > branch?  TIA.
> 
> Done!

Thanks.