[libcxx] Fix std::vector construct_iter_iter.pass.cpp test (C++98/03)

The test is failing on 32-bit targets in C++03 mode. Clang produces
the following warning: 'integer literal is too large to be represented
in type 'long' and is subject to undefined behavior under C++98,
interpreting as 'unsigned long'; this literal will have type 'long
long' in C++11 onwards [-Wc++11-compat]' which is promoted to an error
and causes the test to fail.

There have been no changes in the test itself since 2019, so it looks
like the diagnostic has been updated.

Differential Revision: https://reviews.llvm.org/D81559

libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp

@@ -180,7 +180,7 @@ void test_ctor_with_different_value_type() {
     // Though the types are different, initialization can be done with `memcpy`.
     int32_t array[1] = { -1 };
     std::vector<uint32_t> v(array, array + 1);
-    assert(v[0] == 4294967295);
+    assert(v[0] == 4294967295U);
   }
 }