re PR libstdc++/80165 (Constexpr tuple of variant doesn't work)

PR libstdc++/80165
* testsuite/20_util/variant/80165.cc: New.

From-SVN: r260209

libstdc++-v3/ChangeLog

+2018-05-13  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+	PR libstdc++/80165
+	* testsuite/20_util/variant/80165.cc: New.
+
 2018-05-10  Jonathan Wakely  <jwakely@redhat.com>
 
 	* doc/xml/faq.xml: Link to C++17 status. Add note to outdated answer.

libstdc++-v3/testsuite/20_util/variant/80165.cc

+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++17 } }
+
+#include <tuple>
+#include <variant>
+
+int main() {
+  using variant_t = std::variant<short, int, long>;
+  constexpr auto variant_v = variant_t{std::in_place_index_t<0>{}, short{}};
+  constexpr auto tuple = std::make_tuple(variant_v);
+  constexpr std::tuple tuple_v{variant_v};
+}