`gcd(a,b) != gcdx(a,b)[1]`

From the documentation I would expect `gcdx`'s first return value to always equal `gcd`'s return value on the same arguments. And yet:

```julia-repl
julia> gcdx(UInt16(100), Int8(-101))
(0x0005, 0xf855, 0x0003)

julia> gcd(UInt16(100), Int8(-101))
0x0001
```

See also #58010
