[GNATS 27353] Set MAX_INTEGER_VALUE/MAX_UNSIGNED_INTEGER_VALUE properly for 128-bit integers #38

Description

​Trying to use a 128-bit integer host representation ends up defaulting MAX_INTEGER_VALUE/MAX_UNSIGNED_INTEGER_VALUE to incorrect values. These seem to work:
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​#define MAX_INTEGER_VALUE ((__int128_t)0x7fffffffffffffffffffffffffffffff)
​#define MAX_UNSIGNED_INTEGER_VALUE ((__uint128_t)0xffffffffffffffffffffffffffffffff)