Add defines to indicate if intypes.h and stdint.h are unavailable

Use the defines OPENSSL_NO_INTTYPES_H & OPENSSL_NO_STDINT_H to determine
if the headers are unavailable for a platform.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8986)