* libc/string/index.c: Include <strings.h> for "index".
* libc/string/rindex.c: Include <strings.h> for "rindex".
* libc/string/strcasecmp.c: Include <strings.h> for "strcasecmp".
Don't include <string.h>.
* libc/string/strncasecmp.c: Include <strings.h> for "strncasecmp".
Don't include <string.h>.
* libc/string/bzero.c: Include <strings.h> for "bzero".
Don't include <string.h>
* libc/misc/ffs.c: Include <strings.h> for "ffs".
Don't include <_ansi.h>.
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