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>

reporter_name="Alexander BIGGA"

reporter_url="http://sourceware.org/ml/crossgcc/2008-07/msg00000.html"

reporter_comment=""