-Ding the bcopy.c source (and similarly strchr from index.c, strrchr
from rindex.c) with stub .c files for memmove, memcpy, strchr and
strrchr that simply #define the appropriate thing and #include the
appropriate .c file. Inspired by the way many m-d .S files handle the
same thing. This radically simplifies the Makefile.inc for libc/string
(and libkern).
