int8_t and uint8_t are definitely not possible on systems with CHAR_BIT greater than 8.
(From 6.2.6.1: Values stored in non-bit-field objects of any other object type consist of n × CHAR_BIT bits, where n is the size of an object of that type, in bytes.)
(From 6.2.6.1: Values stored in non-bit-field objects of any other object type consist of n × CHAR_BIT bits, where n is the size of an object of that type, in bytes.)