[libcxx] [test] Include <algorithm> in string_view::copy test

[BillyONeal]

Summary

The string_view::copy test calls std::min, which is not required to be
made available by including <string_view>.

(The MSVC++ STL does not use std::min internally because we need to
avoid the *macro* named min which is defined by windows.h)

[EricWF]

@BillyONeal Do you have commit access?

[BillyONeal]

No, I don't believe any of us in MSVC++ land have commit access.

[EricWF]

r285012.

test/std/strings/string.view/string.view.ops/copy.pass.cpp

 // Throws: out_of_range if pos > size().
 // Remarks: Let rlen be the smaller of n and size() - pos.
 // Requires: [s, s+rlen) is a valid range.
 // Effects: Equivalent to std::copy_n(begin() + pos, rlen, s).
 // Returns: rlen.
 
 
 #include <string_view>
+#include <algorithm>
 #include <cassert>
 
 #include "test_macros.h"
 
 template<typename CharT>
 void test1 ( std::basic_string_view<CharT> sv, size_t n, size_t pos ) {
     const size_t rlen = std::min ( n, sv.size() - pos );