Remove dependence on `__builtin_*_overflow` builtins in generated C

[ashn-dot-dev]

Currently, addition, subtraction, and multiplication rely on the GCC/Clang builtins __builtin_add_overflow, __builtin_sub_overflow, __builtin_mul_overflow. Replace these builtins with an strictly standards compliant versions wrapping arithmetic functions.

Resources:

• C99 compliant bit twiddling hack
• C23 stdckdint.h's ckd_add, ckd_sub, and ckd_mul