Don't rely on `HAVE_' macros in public header "tags.h".

Don't rely on `HAVE_' macros in public header "tags.h".

* configure.ac: Check for `intptr_t' and `uintptr_t'.  Substitute
  `SCM_I_GSC_T_INTPTR' and `SCM_I_GSC_T_UINPTR'.

* libguile/__scm.h (SCM_T_UINTPTR_MAX, SCM_T_INTPTR_MIN,
  SCM_T_INTPTR_MAX): New macros.

* libguile/_scm.h (SIZEOF_SCM_T_BITS): New macro.

* libguile/gen-scmconfig.c (main): Produce typedefs for `scm_t_intptr'
  and `scm_t_uintptr'.

* libguile/gen-scmconfig.h.in (SCM_I_GSC_T_INTPTR, SCM_I_GSC_T_UINPTR):
  New macros.

* libguile/tags.h: Don't check for `HAVE_INTTYPES_H' and
  `HAVE_STDINT_H'; don't include <inttypes.h> nor <stdint.h>.
  (scm_t_signed_bits, scm_t_bits): Define unconditionally as aliases for
  `scm_t_intptr' and `scm_t_uintptr', respectively.
  (SCM_T_SIGNED_BITS_MAX, SCM_T_SIGNED_BITS_MIN, SCM_T_BITS_MAX):
  Likewise.
  (SIZEOF_SCM_T_BITS): Remove.