Revert "Revert "Update aosp/master libcxx rebase to r263688""

This reverts commit 1d4a1edbc7.

Change-Id: I2909937fe582f2c5552bc86e7f4d2d5cff0de0aa

test/std/strings/basic.string/string.cons/default_noexcept.pass.cpp

@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03
+
 // <string>
 
 // basic_string()
@@ -29,7 +31,6 @@ struct some_alloc
 
 int main()
 {
-#if __has_feature(cxx_noexcept)
     {
         typedef std::string C;
         static_assert(std::is_nothrow_default_constructible<C>::value, "");
@@ -42,5 +43,4 @@ int main()
         typedef std::basic_string<char, std::char_traits<char>, some_alloc<char>> C;
         static_assert(!std::is_nothrow_default_constructible<C>::value, "");
     }
-#endif
 }