PATCH: PR gas/12409: --compress-debug-sections doesn't work on empty DWARF sections

[Cary Coutant]

> Should I apply this patch? Since the compression header is 12 byte,
> if the section is smaller than 12 bytes, compressed section will be
> bigger.

It's fine with me. You may also want to check whether the compressed
bits actually come out smaller than the uncompressed bits. The test
you've added here is just a trivial case of the more general one.

The reason I didn't do this originally was so that we wouldn't end up
with a mixture of compressed and uncompressed sections in one file,
for fear of what effect that might have on downstream tools. With the
bfd and linker changes we have, I think this is safe now.

-cary