From: Seija Kijin <doremylover123@gmail.com>

Use pthread_exit instead of async_exit.

This means we do not have
to deal with Windows's implementation
requiring an unsigned exit coded
despite the POSIX exit code requiring
a signed exit code.

Use _beginthreadex instead of CreateThread
since we use the Windows CRT.

Finally, check for NULL handles, not "INVALID_HANDLE,"
as _beginthreadex guarantees a valid handle in most cases

Signed-off-by: Seija Kijin <doremylover123@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1440.git.git.1674334159116.gitgitgadget@gmail.com