setup paddle on redhat

[sunshinee24]

Is there anyone setting up paddle on redhat, in cmake/extern/system file, it seems paddle doesn't support redhat, I am not sure.

[gangliao]

@sunshinee24
This PR can help to pass system detection in CMake.
#1195

We have yet to build Paddle on red hat. But, you can try it on red hat.

[wangkuiyi]

Currently, the society supports only two forms of builds -- Docker images and Ubuntu 14.04. It would be great if you are able to build and run Paddle on RedHat/Fedora and would like to maintain it (answering related users's inquiries). If so, could we have your favor to create a Pull Request adding a https://github.com/PaddlePaddle/Paddle/tree/develop/doc/howto/redhat/README.md file describing the steps to build and run Paddle on RedHat? Thanks.