build: Use modern Autoconf check for type.
* configure.ac (byte, ushort, us6, u32, u64): Use AC_CHECK_TYPES. * cipher/poly1305.c: Use HAVE_TYPE_U64. * src/hmac256.c: HAVE_TYPE_U32. * src/types.h: Use HAVE_TYPE_BYTE, HAVE_TYPE_USHORT, HAVE_TYPE_U16, HAVE_TYPE_U32, and HAVE_TYPE_U64.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>