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

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

add support to gcc for AES and PCLMUL intrinsics... This addes the
-maes option, but not the -mpclmul option as I ran out of bits in
the 32 bit flags field... You can -D__PCLMUL__ to get this, but it
won't be compatible w/ clang and modern gcc...

Reviewed by: -current, -toolchain