Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

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

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Add the llvm-cov and llvm-profdata tools, when WITH_CLANG_EXTRAS is
defined. These help with processing coverage and profile data.

Vendor import of llvm RELEASE_360/rc1 tag r226102 (effectively, 3.6.0 RC1):
https://llvm.org/svn/llvm-project/llvm/tags/RELEASE_360/rc1@226102