JDK-8263721 uses `nullptr_t` in the global namespace. This is fine, since "nullptr_t is available in the global namespace when <stddef.h> is included" from https://en.cppreference.com/w/cpp/types/nullptr_t.

However, the clang+libstdc++ combination does not work. The pure clang chain (clang+libc++) works fine, so one could argue this is a "user bug", not a clang bug. More details are covered at https://codereview.chromium.org/1558333002.

Considering that clang+libstdc++ is not a uncommont combination, maybe it's better to revise the code to make that combination work.

One workaround is to add the following to `globalDefinitions.hpp`:

```
#include <cstddef>
using nullptr_t = std::nullptr_t;
```