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="Yann E. MORIN"

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

reporter_comment="EXPERIMENTAL MIPS-64 n64 toolchain."