I can't reproduce the problem on the main branch:
| Pike v7.9 release 5 running Hilfe v3.5 (Incremental Pike Frontend) | > -0x7fffffff; | (1) Result: -2147483647 | > -0x7fffffff - 1; | (2) Result: -2147483648 | > -0x7fffffff - 2; | (3) Result: -2147483649 | > Pike.get_runtime_info(); | (4) Result: ([ /* 6 elements */ | "abi": 64, | "auto_bignum": 1, | "bytecode_method": "amd64", | "float_size": 64, | "int_size": 64, | "native_byteorder": 1234 | ])