x86: insn decoder test checks objdump version

Check objdump version before using it for insn decoder build test,
because some older objdump can't decode AVX code correctly.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Jim Keniston <jkenisto@us.ibm.com>
LKML-Reference: <20091120171314.6715.30390.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>