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