[libc++] Add some tests for std::bit_cast using pointers

libcxx/test/std/numerics/bit/bit.cast/bit_cast.pass.cpp

 #endif
 #if defined(__SIZEOF_INT128__) && __SIZEOF_LONG_DOUBLE__ == __SIZEOF_INT128__ &&                                       \
     !TEST_HAS_FEATURE(memory_sanitizer) // Some bits are just padding.
         test_roundtrip_through<__int128_t, false>(i);
         test_roundtrip_through<__uint128_t, false>(i);
 #endif
     }
 
+    // Test pointers
+    {
+        {
+            int obj = 3;
+            void* p = &obj;
+            test_roundtrip_through_nested_T(p);
+            test_roundtrip_through_buffer(p);
+            test_roundtrip_through<void*>(p);
+            test_roundtrip_through<char*>(p);
+            test_roundtrip_through<int*>(p);
+        }
+        {
+            int obj = 3;
+            int* p = &obj;
+            test_roundtrip_through_nested_T(p);
+            test_roundtrip_through_buffer(p);
+            test_roundtrip_through<int*>(p);
+            test_roundtrip_through<char*>(p);
+            test_roundtrip_through<void*>(p);
+        }
+    }
+
     return true;
 }
 
 // TODO: There doesn't seem to be a way to perform non-trivial correctness
 //       tests inside constexpr.
 constexpr bool basic_constexpr_test() {
     struct Nested { char buffer[sizeof(int)]; };
     int from = 3;