elf_getarhdr.c: Return correct header for archive within an archive

elf_getarhdr.c: Return correct header for archive within an archive

If elf_getarhdr is called on a descriptor that refers to an archive
which is itself a member of another archive, it may return the Elf_Arhdr
of the current member (i.e., the member selected by elf_next or elf_rand)
of the inner archive instead of Elf_Arhdr of the inner archive itself.

This also causes a memory leak: elf_end only attempts to free
Elf_Arhdr fields ar_name and ar_rawname for descriptors that are not
ELF_K_AR.

To fix this, replace the state.elf[32|64] field elf_ar_hdr with new
struct Elf field elf_ar_hdr.  This field stores the Elf_Arhdr for all
descriptors of archive members, including those with kind ELF_K_AR.

Also rename the state.ar field elf_ar_hdr to cur_ar_hdr to clarify that
this is the header of an archive's current member.

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