Clean up CMake

[curtpm]

No description provided.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[PaulRashidi]

Miss the c++11 flag?

[curtpm]

added the CXX_STANDARD_REQUIRED flag.

[suikki]

Both CMAKE_CXX_STANDARD and CXX_STANDARD_REQUIRED require min cmake 3.1 so cmake_minimum_required should be bumped too.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

[curtpm]

I signed it!

[PaulRashidi]

Please read the above carefully. You may be creating commit messages with one email address and signing the CLA with another email address. If this isn't the case, after you've double checked, let us know and we'll look into it.

Thanks!