* string/strings.h: Do not suppress the file if string.h has
already been included.
(bcmp, bcopy, bzero, strcasecmp, strncasecmp): Add __nonnull
annotations.
(index, rindex): Define inline forwarders even if
__CORRECT_ISO_CPP_STRING_H_PROTO is defined.
(ffs): Use __attribute_const__.
(ffsl, ffsll): Declare here.
(strcasecmp_l, strncasecmp_l): Correct comments; these functions
have now been standardized.