elf: Ignore SHF_COMPRESSED sections
some newer systems have debug sections compressed by default, which
includes those in the crt[1in].o startup files. These can't simply
be concatenated like all others (which leads to invalid section contents
ultimately making gdb fail) but need special handling.
Instead of that special handling (decompressing, which in turn requires
linking against zlib) let's just ignore such sections, even though that
means to also ignore all other debug sections from that particular input
file. Our own generated files of course don't have the problem.