debug/gdb: fix canadian-cross in case of static cross gdb

Building the cross-gdb shoud be done using the host compiler,
not the native compiler.

Reported-by: Per Arnold Blaasmo <per-arnold.blaasmo@atmel.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 #!/bin/sh

 set -e

 printf "Running autoconf...\n"

 autoconf -Wall --force

 printf "Done. You may now run:\n    ./configure\n"