libelf: Explicitly update section data after (de)compression.

libelf: Explicitly update section data after (de)compression.

We need to explictly trigger a section data reload after updating the
ELF section rawdata to make sure it gets written out to disk on an
elf_update. Doing this showed one bug/inefficiently when the underlying
file has a different endianness. In that case for debug sections we
would convert by allocating a new buffer and just copying over the
raw data into a new buffer. This is not really necessary and would
hide any relocations done on the rawdata by libdwfl.

Added a couple of new ppc64 big endian testfiles that show the issue.

Signed-off-by: Mark Wielaard <mark@klomp.org>