WIP: Improve testing of exception handling.

Move elision was happening and could render the tests useless.
Also take the occasion in this patch to handle all algorithms.
Can easily(?) be landed before the rest.

Author: ldionne

libcxx/test/std/algorithms/numeric.ops/reduce/pstl.exception_handling.pass.cpp

@@ -38,6 +38,7 @@ int main(int, char**) {
       int a[2]{};
       (void)std::reduce(policy, std::begin(a), std::end(a), 1, [](int, int) -> int { throw 1; });
     });
+
     EXPECT_STD_TERMINATE([&] {
       try {
         int a[] = {1, 2};

libcxx/test/std/algorithms/numeric.ops/transform.reduce/pstl.exception_handling.pass.cpp

@@ -26,33 +26,43 @@ int main(int, char**) {
     EXPECT_STD_TERMINATE([&] {
       try {
         int a[] = {1, 2};
-        (void)std::transform_reduce(
-            policy,
-            util::throw_on_move_iterator(std::begin(a), 1),
-            util::throw_on_move_iterator(std::end(a), 1),
-            util::throw_on_move_iterator(std::begin(a), 1),
-            1);
+        util::throw_on_move_iterator first1(std::begin(a), 1);
+        util::throw_on_move_iterator last1(std::end(a), 1);
+        util::throw_on_move_iterator first2(std::begin(a), 1);
+        (void)std::transform_reduce(policy, std::move(first1), std::move(last1), std::move(first2), 1);
       } catch (const util::iterator_error&) {
         assert(false);
       }
       std::terminate(); // make the test pass in case the algorithm didn't move the iterator
     });
 
     EXPECT_STD_TERMINATE([&] {
-      int a[2]{};
+      int a[] = {1, 2};
       (void)std::transform_reduce(
           policy, std::begin(a), std::end(a), 1, [](int, int) -> int { throw 1; }, [](int) -> int { return 0; });
     });
+
+    EXPECT_STD_TERMINATE([&] {
+      try {
+        int a[] = {1, 2};
+        util::throw_on_move_iterator first1(std::begin(a), 1);
+        util::throw_on_move_iterator last1(std::end(a), 1);
+        (void)std::transform_reduce(policy, std::move(first1), std::move(last1), 1, std::plus{}, [](int) -> int {
+          return 0;
+        });
+      } catch (const util::iterator_error&) {
+        assert(false);
+      }
+      std::terminate(); // make the test pass in case the algorithm didn't move the iterator
+    });
+
     EXPECT_STD_TERMINATE([&] {
       try {
         int a[] = {1, 2};
-        (void)std::transform_reduce(
-            policy,
-            util::throw_on_move_iterator(std::begin(a), 1),
-            util::throw_on_move_iterator(std::end(a), 1),
-            1,
-            std::plus{},
-            [](int) -> int { return 0; });
+        util::throw_on_move_iterator first1(std::begin(a), 1);
+        util::throw_on_move_iterator last1(std::end(a), 1);
+        util::throw_on_move_iterator first2(std::begin(a), 1);
+        (void)std::transform_reduce(policy, std::move(first1), std::move(last1), std::move(first2), 1);
       } catch (const util::iterator_error&) {
         assert(false);
       }