strip: Ignore --reloc-debug-sections-only for non-ET_REL files.

strip: Ignore --reloc-debug-sections-only for non-ET_REL files.

strip --reloc-debug-sections-only is expected to be a no-op for
non-ET_REL files.  This was not enforced in the code.  Sections
were copied over to a new output file and normally its contents
would be identical to the input file.

However the output file is not identical to a non-ET_REL input
file if the linker organized sections such that the indices of
SHF_ALLOC sections are not in a contigous group.

In this case strip will modify sections in order to keep all SHF_ALLOC
sections in a contiguous group.

Fix this by ignoring --reloc-debug-sections-only for non-ET_REL files.

https://sourceware.org/bugzilla/show_bug.cgi?id=32253

Signed-off-by: Aaron Merey <amerey@redhat.com>