debug/gdb: enforce gdbserver cross-compilation

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Message-Id: <ca85cad85c4dd20e74f1.1363446262@laptop>
Patchwork-Id: 228219

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/"

reporter_comment="Toolchain for the Raspberry Pi, with hard-float."