copysym: Avoid dependency on <stdint.h>

The <inttypes.h> header is older and a bit more portable.  But even
then, it is not really essential for this code.  So adjust things to
use <inttypes.h> only if the Autoconf-provided HAVE_INTTYPES_H is
defined; otherwise a C89 <limits.h>-based fallback is used.