locale.c: don't use strcpy()

locale.c: don't use strcpy()

A recent commit added a strcpy() to locale.c.

This is Frowned Upon, and was making porting/libperl.t fail.

Since PL_strxfrm_min_char appears to be a 3-byte buffer, I've just changed
it to manually copy 3 individual bytes - which is probably more efficient
than a full-blown Copy(). But I haven't looked closely at whether this is
correct - this is more of quick fix to get smoking passing again.