amd64: convert libc bcopy to a C func to avoid future bloat

[mjg]

Summary

The function is of limited use and is an almost a direct clone of memmove/memcpy (with arguments swapped). Introduction of ERMS variants of string routines would mean avoidable growth of libc.

bcopy will get redefined to a __builtin_memmove later on with this symbol only left for compatibility.

memcpy and memmove are now implemented separately.

[kib]

lib/libc/amd64/string/bcopy.c

5

Please change to __FBSDID

9

string.h includes strings.h.