POSIX.1-2008 specifies that those two functions should be declared by
including <strings.h>, not <string.h> (the latter only has strcoll_l()
and strxfrm_l()):
http://pubs.opengroup.org/onlinepubs/9699919799/functions/strcasecmp.html
Obtained from: DragonFlyBSD
Reviewed by: theraven
MFC after: 2 weeks