Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Use <osreldate.h> rather than the OS version reported by the kernel
to determine which Elf Types are to be handled. Change the M4
templates to wrap an `#if __FreeBSD_version >= NNN'/`#endif' pair
around the generated code for each ELF data type, where `NNN' is
the OS version where the ELF type was added to the source tree.

This change allows cross-builds of old sources on newer FreeBSD
systems to work correctly.

Problem reported by: ru

MFP4: Add an implementation of the ELF(3) and GELF(3) API set.

Bump __FreeBSD_version.

Reviewed by: jb