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

Allow us to build clang for ARM EABI. Clang and llvm use the
arm-gnueabi-freebsd10.0 triple for EABI. Use this when we are on arm or
armv6 and are building for EABI.

Reviewed by: dim

Add a WITH_CLANG_EXTRAS option for src.conf(5), disabled by default,
that builds the following additional llvm/clang tools:

- bugpoint
- llc
- lli
- llvm-ar
- llvm-as
- llvm-bcanalyzer
- llvm-diff
- llvm-dis
- llvm-extract
- llvm-ld
- llvm-link
- llvm-mc
- llvm-nm
- llvm-objdump
- llvm-prof
- llvm-ranlib
- llvm-rtdyld
- llvm-stub
- macho-dump
- opt

These tools are mainly useful for people that want to manipulate llvm
bitcode (.bc) and llvm assembly language (.ll) files, or want to tinker
with llvm and clang themselves.

MFC after: 2 weeks