Build mmproxy on CentOS 7 (Non-issue)

Hi,

I just want to share my building script:

https://gist.github.com/shikendon/f23a36c3b93032db1079efe677248f6b
```bash
#!/usr/bin/env bash
set -e

cat <<'END' | sudo tee /etc/yum.repos.d/epel-alonid-llvm.repo
[epel-alonid-llvm-3.9.0]
name=Copr repo for llvm-3.9.0 owned by alonid
baseurl=https://copr-be.cloud.fedoraproject.org/results/alonid/llvm-3.9.0/epel-7-$basearch/
type=rpm-md
enabled=0
gpgkey=https://copr-be.cloud.fedoraproject.org/results/alonid/llvm-3.9.0/pubkey.gpg
gpgcheck=1
repo_gpgcheck=0
enabled_metadata=1
skip_if_unavailable=True
END
sudo rpm --import https://copr-be.cloud.fedoraproject.org/results/alonid/llvm-3.9.0/pubkey.gpg

sudo yum -y groupinstall "Development Tools"
sudo yum -y install --enablerepo=epel-alonid-llvm-3.9.0 clang-3.9.0
sudo yum -y install glibc-static
sudo ln -s -f /opt/llvm-3.9.0/bin/* /usr/bin

git clone https://github.com/cloudflare/mmproxy.git --recursive
pushd mmproxy
make # If failed, try to build libmill manually: `pushd libmill && ./configure && make`
find `pwd` -type f -executable -name mmproxy
```

It took me a half day. Hope this can save someone's time.

Great work mmproxy 👍