debug/gdb: fix for psim build failure due to -lz in gdb-7.2.

Signed-off-by: "Horst Kronstorfer" <horst.kronstorfer@aon.at>
[yann.morin.1998@anciens.enib.fr: fix space-damage]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Nye Liu"

reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

reporter_comment=""