This function is used by LibreSSL and OpenSSH and is provided by the
OpenBSD libc.
* libc/include/string.h (timingsafe_memcmp): Declare.
* libc/string/timingsafe_memcmp.c: New file.
* libc/string/Makefile.am: Add new file.
* libc/string/Makefile.in: Regenerate.
Sebastian Huber