crypto: store thread id as pointer-sized

In https://github.com/MSOpenTech/libuv/commit/59658a8de7cc05a58327a164fd2ed4b050f8b4f4
the return of uv_thread_self() was changed from unsigned long to
uv_thread_t.

uv_thread_t is a HANDLE (pointer-sized) on Windows, which means that it
cannot be stored with CRYPTO_THREADID_set_numeric without data loss.