debug/gdb: update Linaro GDB revision for 2013.05

Update Linaro GDB with the latest available revision.

Signed-off-by: "Michael Hope" <michaelh@juju.net.nz>
Message-Id: <bea34f42853a9d87a628.1372452016@localhost>
Patchwork-Id: 255667

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""