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

Update libc++ to 3.8.0. Excerpted list of fixes (with upstream revision
numbers):

r242679 Implement the plugin-based version of std::search. There are no
searchers yet; those are coming soon.
r242682 Implement the default searcher for std::experimental::search.
r243728 Add <experimental/any> v2.
r245330 implement more of N4258 - Cleaning up noexcept in the standard
library. Specifically add new noexcept stuff to vector and
string's move-assignment operations
r245334 Fix PR22606 - Leak pthread_key with static storage duration to
ensure all of thread-local destructors are called.
r245335 Fix PR23589: std::function doesn't recognize null pointer to
varargs function.
r247036 Implementation of Boyer-Moore and Boyer-Moore-Horspool
searchers for the LFTS.
r249325 Implement LWG#2063, and update the issues links to point to the
github generated pages
r249738 Split <ctype.h> out of <cctype>.
r249739 Split <errno.h> out of <cerrno>.
r249740 Split <float.h> out of <cfloat>.
r249741 Split <inttypes.h> out of <cinttypes>.
r249742 Split <math.h> out of <cmath>.
r249743 Split <setjmp.h> out of <csetjmp>.
r249761 Split <stddef.h> out of <cstddef>.
r249798 Split <stdio.h> out of <cstdio>.
r249800 Split <stdlib.h> out of <cstdlib>.
r249889 Split <wchar.h> out of <cwchar>.
r249890 Split <wctype.h> out of <cwctype>.
r249929 Split <string.h> out of <cstring>.
r250254 ABI versioning macros for libc++.
r251246 Fix LWG#2244: basic_istream::seekg
r251247 Fix LWG#2127: Move-construction with raw_storage_iterator.
r251253 Fix LWG#2476: scoped_allocator_adaptor is not assignable
r251257 Fix LWG#2489: mem_fn() should be noexcept
r251618 Implement P0004R1 'Remove Deprecated iostreams aliases'
r251766 Implement the first part of P0006R0: Adopt Type Traits Variable
Templates for C++17.
r252195 Implement P0092R1 for C++1z
r252350 Allow deque to handle incomplete types.
r252406 More of P0006R0: type traits variable aliases for C++17.
r252407 Implement LWG#2353: std::next is over-constrained
r252905 Implement P0074: Making owner_less more flexible
r253215 Implement P0013R1: Logical Operator Type Traits.
r253274 Implement P0007: Constant View: A proposal for a std::as_const
helper function template.
r254119 Add static_assert to set/multiset/map/multimap/forward_list/deque
that the allocator's value_type match the container's value_type.
r254283 Implement more of P0006; Type Traits Variable Templates.
r255941 LWG2485: get() should be overloaded for const tuple&&.
r256325 Fix LWG Issue #2367 - Fixing std::tuple and std::pair's default
constructors.
r256652 Fix for ALL undefined behavior in <list>.
r256859 First half of LWG#2354: 'Unnecessary copying when inserting
into maps with braced-init syntax'

Exp-run: antoine
Relnotes: yes

Vendor import of libc++ release_38 branch r258549:
https://llvm.org/svn/llvm-project/libcxx/branches/release_38@258549

Vendor import of libc++ trunk r256633:
https://llvm.org/svn/llvm-project/libcxx/trunk@256633