- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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