Import libc++ trunk r224926. This fixes a number of bugs, completes

Import libc++ trunk r224926.  This fixes a number of bugs, completes
C++14 support[1], adds more C++1z features[2], and fixes the following
LWG issues[3]:

1450: Contradiction in regex_constants
2003: String exception inconsistency in erase.
2075: Progress guarantees, lock-free property, and scheduling
      assumptions
2104: unique_lock move-assignment should not be noexcept
2112: User-defined classes that cannot be derived from
2132: std::function ambiguity
2135: Unclear requirement for exceptions thrown in
      condition_variable::wait()
2142: packaged_task::operator() synchronization too broad?
2182: Container::[const_]reference types are misleadingly specified
2186: Incomplete action on async/launch::deferred
2188: Reverse iterator does not fully support targets that overload
      operator&
2193: Default constructors for standard library containers are explicit
2205: Problematic postconditions of regex_match and regex_search
2213: Return value of std::regex_replace
2240: Probable misuse of term "function scope" in [thread.condition]
2252: Strong guarantee on vector::push_back() still broken with C++11?
2257: Simplify container requirements with the new algorithms
2258: a.erase(q1, q2) unable to directly return q2
2263: Comparing iterators and allocator pointers with different
      const-character
2268: Setting a default argument in the declaration of a member
      function assign of std::basic_string
2271: regex_traits::lookup_classname specification unclear
2272: quoted should use char_traits::eq for character comparison
2278: User-defined literals for Standard Library types
2280: begin / end for arrays should be constexpr and noexcept
2285: make_reverse_iterator
2288: Inconsistent requirements for shared mutexes
2291: std::hash is vulnerable to collision DoS attack
2293: Wrong facet used by num_put::do_put
2299: Effects of inaccessible key_compare::is_transparent type are not
      clear
2301: Why is std::tie not constexpr?
2304: Complexity of count in unordered associative containers
2306: match_results::reference should be value_type&, not const
      value_type&
2308: Clarify container destructor requirements w.r.t. std::array
2313: tuple_size should always derive from integral_constant<size_t, N>
2314: apply() should return decltype(auto) and use decay_t before
      tuple_size
2315: weak_ptr should be movable
2316: weak_ptr::lock() should be atomic
2317: The type property queries should be UnaryTypeTraits returning
      size_t
2320: select_on_container_copy_construction() takes allocators, not
      containers
2322: Associative(initializer_list, stuff) constructors are
      underspecified
2323: vector::resize(n, t)'s specification should be simplified
2324: Insert iterator constructors should use addressof()
2329: regex_match()/regex_search() with match_results should forbid
      temporary strings
2330: regex("meow", regex::icase) is technically forbidden but should
      be permitted
2332: regex_iterator/regex_token_iterator should forbid temporary
      regexes
2339: Wording issue in nth_element
2341: Inconsistency between basic_ostream::seekp(pos) and
      basic_ostream::seekp(off, dir)
2344: quoted()'s interaction with padding is unclear
2346: integral_constant's member functions should be marked noexcept
2350: min, max, and minmax should be constexpr
2356: Stability of erasure in unordered associative containers
2357: Remaining "Assignable" requirement
2359: How does regex_constants::nosubs affect basic_regex::mark_count()?
2360: reverse_iterator::operator*() is unimplementable

[1] http://libcxx.llvm.org/cxx1y_status.html
[2] http://libcxx.llvm.org/cxx1z_status.html
[3] http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html

Exp-run:	antoine
MFC after:	1 month