Silence valgrind on safe reads beyond potential array bounds. * lib/rawmemchr.valgrind: New file. * lib/strchrnul.valgrind: Likewise. * modules/rawmemchr (Files): Distribute new file. * modules/strchrnul (Files): Likewise. Suggested by Bruno Haible. Signed-off-by: Eric Blake <ebb9@byu.net>