[diffoscope] Need a way to select objdump for different architectures

[Martin Husemann]

Hi folks,

I am trying to use diffoscoe to find differences in builds generated for
atari and this is quite tricky due to the native objdump not being able
to decode atari elf binaries.

The suggested workaround in

	https://salsa.debian.org/reproducible-builds/diffoscope/-/issues/375

does not work with current diffoscope, if I make the m68k objdump available
as "objdump" in some dir in my $PATH early diffoscope will fail to start
up at all - apparently the ffi code accessing libarchive.so requires a
native objdump.

So I am lost, short of hacking the installed script (which I did for now)
like this (in the python site-packages diffoscope/comparators/elf.py):

    @tool_required("objdump")
    def cmdline(self):
        return (
            # HACK: hard code path to proper cross-objdump
            # [get_tool_name("objdump")]
            ['/home/builds/ab/HEAD/atari/20250703130037Z-tools/bin/m68k--netbsdelf-objdump']
            + self.objdump_options()
            + ["--section={}".format(self._section_name), self.path]
        )

Would be cool if that path could be overriden by a command line option.

Martin