configure: add checks for objcopy and objdump

These two went MIA after the migration to an autoconf-based ./configure.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

reporter_name="Ioannis E. Venetis"

reporter_url="http://sourceware.org/ml/crossgcc/2011-05/msg00005.html"

reporter_comment=""