Support mips/mipsle/mips64/mips64le GOARCH

[maddie]

Currently it seems this library doesn't support mips/mipsle/mips64/mips64le, when compiling the following error would appear:

# github.com/creack/goselect
../../../github.com/creack/goselect/fdset.go:14:14: undefined: NFDBITS
../../../github.com/creack/goselect/fdset.go:19:14: undefined: NFDBITS
../../../github.com/creack/goselect/fdset.go:24:21: undefined: NFDBITS

Manually adding mips/mipsle to fdset_32.go and mips64/mips64le to fdset_64.go build flag seems to compile successfully, however I'm not sure if this is the correct way to do it.

If it's OK to solve the problem like I mentioned above, I would be happy to send in a PR.

Thanks!

[creack]

I don't have a mips platform available so can't test it, but if your change works and the tests pass, then go for it and submit a PR, it is more than welcome :)

[maddie]

PR submitted, thanks!