Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use calloc().

MFC after: 2 weeks

Remove unneeded reference to link.h (sys/link_elf.h).

MFC after: 2 weeks

fix a couple of innocuous compiler warnings

MFC after: 3 days

Use posix_memalign() rather than assuming that malloc() provides adequate
alignment.

Approved by: markm (mentor)

Make our ELF64 type definitions match standards. In particular this
means:
o Remove Elf64_Quarter,
o Redefine Elf64_Half to be 16-bit,
o Redefine Elf64_Word to be 32-bit,
o Add Elf64_Xword and Elf64_Sxword for 64-bit entities,
o Use Elf_Size in MI code to abstract the difference between
Elf32_Word and Elf64_Word.
o Add Elf_Ssize as the signed counterpart of Elf_Size.

MFC after: 2 weeks

Explicitly pass in the relocation base and data offset into ef_reloc()
rather than relying on a trick that happens to work for the current
relocation schemes. Also add some comments and improve variable
naming.

Use a temporary void * variable to work around a strict aliasing
warning that gcc generates at -O2 and higher.

Add support for reading ELF relocatable object file format modules.