[libc++][test] Enable some more string_view tests

[jloser]

Summary

Some test cases for ends_with.ptr.pass and starts_with.ptr.pass for
string_view are commented out, but work just fine. Uncomment them.

libcxx/test/std/strings/string.view/string.view.template/ends_with.ptr.pass.cpp

 int main(int, char**)
 {
     {
     typedef std::string_view SV;
     const char *s = "abcde";
     SV  sv0 {};
     SV  sv1 { s + 4, 1 };
     SV  sv2 { s + 3, 2 };
-//     SV  sv3 { s + 2, 3 };
-//     SV  sv4 { s + 1, 4 };
-//     SV  sv5 { s    , 5 };
+    SV  sv3 { s + 2, 3 };
+    SV  sv4 { s + 1, 4 };
+    SV  sv5 { s    , 5 };
     SV  svNot {"def", 3 };
 
     LIBCPP_ASSERT_NOEXCEPT(sv0.ends_with(""));
 
     assert ( sv0.ends_with(""));
     assert (!sv0.ends_with("e"));
 
     assert ( sv1.ends_with(""));

libcxx/test/std/strings/string.view/string.view.template/starts_with.ptr.pass.cpp

 int main(int, char**)
 {
     {
     typedef std::string_view SV;
     const char *s = "abcde";
     SV  sv0 {};
     SV  sv1 { s, 1 };
     SV  sv2 { s, 2 };
-//     SV  sv3 { s, 3 };
-//     SV  sv4 { s, 4 };
-//     SV  sv5 { s, 5 };
+    SV  sv3 { s, 3 };
+    SV  sv4 { s, 4 };
+    SV  sv5 { s, 5 };
     SV  svNot {"def", 3 };
 
     LIBCPP_ASSERT_NOEXCEPT(sv0.starts_with(""));
 
     assert ( sv0.starts_with(""));
     assert (!sv0.starts_with("a"));
 
     assert ( sv1.starts_with(""));