Minor cleanup for string_view; mostly from suggestions by Richard Smith. Also, make the tests pass under c++03

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@212185 91177308-0d34-0410-b5e6-96231b3b80d8
Fix some failing tests for the standard containers. The tests were failing in 32-bit mode because they assumed that std::size_type and make_unsigned<ptrdiff_t>::type were always the same type. No change to libc++, just the tests.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@212538 91177308-0d34-0410-b5e6-96231b3b80d8
string_view enhancements. Move to the correct namespace. Better constexpr support (thanks to Richard for the suggestions). Update the tests to match this. Add <experimental/__config for experimental macros/etc to live.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@212569 91177308-0d34-0410-b5e6-96231b3b80d8
Add a reset method to the counting predicates in the test suite

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@212651 91177308-0d34-0410-b5e6-96231b3b80d8