The actual `zig objcopy` does not accept keeping multiple sections.
If you pass multiple `-j .section` arguments to `zig objcopy`, it will
only respect the last one passed.
Originally I changed `zig objcopy` to accept multiple sections
and then concatenate them instead of returning after outputting the
first section (see emitElf) but I realized concatenating probably doesn't make sense.
aef66eebe3