[libc++][test] std::variant test cleanup

* Add the conventional `return 0` to `main` in `variant.assign/conv.pass.cpp` and `variant.ctor/conv.pass.cpp`

* Fix some MSVC signed-to-unsigned conversion warnings by replacing `int` literarls with `unsigned int` literals

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@374723 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/variant/variant.variant/variant.assign/conv.pass.cpp

@@ -40,4 +40,5 @@ int main(int, char**)
   static_assert(!std::is_assignable<std::variant<bool>, std::unique_ptr<char> >::value, "");
   static_assert(!std::is_assignable<std::variant<bool>, decltype(nullptr)>::value, "");
 
+  return 0;
 }

test/std/utilities/variant/variant.variant/variant.assign/copy.pass.cpp

@@ -453,7 +453,7 @@ void test_copy_assignment_different_index() {
   {
     using V = std::variant<int, CopyAssign, unsigned>;
     CopyAssign::reset();
-    V v1(std::in_place_type<unsigned>, 43);
+    V v1(std::in_place_type<unsigned>, 43u);
     V v2(std::in_place_type<CopyAssign>, 42);
     assert(CopyAssign::copy_construct == 0);
     assert(CopyAssign::move_construct == 0);

test/std/utilities/variant/variant.variant/variant.assign/move.pass.cpp

@@ -462,7 +462,7 @@ void test_move_assignment_different_index() {
     struct {
       constexpr Result<long> operator()() const {
         using V = std::variant<int, TMoveAssign, unsigned>;
-        V v(std::in_place_type<unsigned>, 43);
+        V v(std::in_place_type<unsigned>, 43u);
         V v2(std::in_place_type<TMoveAssign>, 42);
         v = std::move(v2);
         return {v.index(), std::get<1>(v).value};

test/std/utilities/variant/variant.variant/variant.ctor/conv.pass.cpp

@@ -38,5 +38,6 @@ int main(int, char**)
   static_assert(!std::is_constructible<std::variant<bool>, std::true_type>::value, "");
   static_assert(!std::is_constructible<std::variant<bool>, std::unique_ptr<char> >::value, "");
   static_assert(!std::is_constructible<std::variant<bool>, decltype(nullptr)>::value, "");
-  
+
+  return 0;
 }

test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp

@@ -145,7 +145,7 @@ void test_basic() {
     assert(&std::get<3>(v) == &z);
     assert(&ref4 == &std::get<3>(v));
     // emplace with multiple args
-    auto& ref5 = v.emplace<5>(3, 'a');
+    auto& ref5 = v.emplace<5>(3u, 'a');
     static_assert(std::is_same_v<std::string&, decltype(ref5)>, "");
     assert(std::get<5>(v) == "aaa");
     assert(&ref5 == &std::get<5>(v));

test/std/utilities/variant/variant.variant/variant.mod/emplace_type_args.pass.cpp

@@ -145,7 +145,7 @@ void test_basic() {
     assert(&std::get<int &&>(v) == &z);
     assert(&ref4 == &std::get<int &&>(v));
     // emplace with multiple args
-    auto& ref5 = v.emplace<std::string>(3, 'a');
+    auto& ref5 = v.emplace<std::string>(3u, 'a');
     static_assert(std::is_same_v<std::string&, decltype(ref5)>, "");
     assert(std::get<std::string>(v) == "aaa");
     assert(&ref5 == &std::get<std::string>(v));