Add ELF compressed section support

[Mark Wielaard <mjw at redhat dot com>]

Hi,

This is hopefully the final patch set to add SHF_COMPRESSED section
support to libelf, libdw and some of the elfutils utilities.

All XXXs in the code have been resolved. There has been a small
interface change (as discussed on the Generic System V Application Binary
Interface mailinglist) to add a ELF_CHF_FORCE flag to elf_compress
and elf_compress_gnu and a slight change in return value (zero now means
that the section wasn't compressed because it wasn't beneficial).

This version also makes it so that libdw and libdwfl functions will
automatically handle compressed ELF sections, extends the eu-readelf
support a little, makes elflint recognize and check compressed sections
and adds a new eu-elfcompress utility that can be used to compress or
uncompress ELF sections.

The code can also be found on the mjw/compress4 branch in git.

Comments welcome.

Kurt, this should solve the issue on Debian powerpc that you were
seeing. If you could test the code on the mjw/compress4 branch that
would be great.

Thanks,

Mark