_addcarry_u64 only available on 64-bit platforms

[arnetheduck]

nim-stint/stint/private/primitives/addcarry_subborrow.nim

Line 104 in 7c81df9

func addcarry_u64(carryIn: Carry, a, b: uint64, sum: var culonglong): Carry {.importc: "_addcarry_u64", intrinsics.}

- on 32-bit platforms this should revert to a 32-bit add-with-carry implementation on 32-bit limbs

This is relevant for extracting primitives into an intops library