MFC r311929:

Don't include <errno.h> in reloc_elf.c, as it includes <stand.h> just
after it, which has a conflicting definition of errno. This leads to
the following warning with clang 4.0.0:

In file included from sys/boot/common/reloc_elf32.c:6:
In file included from sys/boot/common/reloc_elf.c:37:
/usr/obj/usr/src/tmp/usr/include/stand.h:155:12: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
extern int errno;
^
sys/sys/errno.h:46:26: note: expanded from macro 'errno'
#define errno (* __error())
^

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

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

Implement elfN(reloc) for powerpc. With this change the kernel is now able to
resolve dependencies of modules at boot time and load additional modules when
needed.

MFC after: 1 week

Add a version of the FreeBSD bootloader which can run in userland, packaged
as a shared library. This is intended to be used by BHyVe to load FreeBSD
kernels into new virtual machines.

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

Separate out the ELF relocation code from the ELF loader, and add
better relocation support for the amd64 and i386 platforms. This
should not result in any change in functionality, but moves a step
towards supporting the relocatable object file modules on amd64.

The same hack/trick as load_elf*.c uses is used here to simultaneously
support both elf32 and elf64 on amd64 and i386.