[libcxx] r276238 - Implement std::string_view as described in http://wg21.link/P0254R1. Reviewed as https://reviews.llvm.org/D21459

[Duncan P. N. Exon Smith via cfe-commits]

> On Jul 20, 2016, at 22:31, Marshall Clow via cfe-commits <cfe-commits at lists.llvm.org> wrote:
> 
> Modified: libcxx/trunk/include/string
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/string?rev=276238&r1=276237&r2=276238&view=diff
> ==============================================================================
> 
> @@ -435,6 +461,7 @@ basic_string<char32_t> operator "" s( co
> */
> 
> #include <__config>
> +#include <string_view>

This breaks the following, valid, C++14 code:

    #include <string>
    #include <experimental/string_view>
    using namespace std;
    using std::experimental::string_view;
    void f() { string_view sv; }

Should <string> #include <string_view> even when we're not in C++17 mode?  Why?

> #include <iosfwd>
> #include <cstring>
> #include <cstdio>  // For EOF.