locale: use memmove for potentially overlapping data

[Paul Eggert]

On 2024-11-06 18:31, DJ Delorie wrote:
> -	  memcpy (ctx->buffer, &ctx->buffer[64], left_over);
> +	  memmove (ctx->buffer, &ctx->buffer[64], left_over);

left_over <= 64 so it's not an overlapping move. Making the change will 
make the code more confusing, as readers might wonder "Why use memmove 
when the move is non-overlapping?"

> Use memmove instead of memcpy just in case

By that argument, shouldn't every call to memcpy be replaced by memmove?