`ipcl_v2.0.0` is incompatible with gcc/g++-8

[fangxiaoran]

Hi @skmono, in this commit aac0eb4#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20a, -Wno-error=deprecated-copy was added as CMAKE_C_FLAGS and CMAKE_CXX_FLAGS.

However, this warning was announced since gcc-9. It's not supported by gcc/g++-8, which is used to build ipcl_python currently within Docker container. This incompatibility leads to a find_package failure as below. Can we just remove it from cmake flags?

[fangxiaoran]

I've tried to use devtoolset-9 to build ipcl_python, rather than devtoolset-8, and it worked. So I think another solution is keeping this flag and updating dependencies in README.

[skmono]

@fangxiaoran Good find. I'll update the compile flags per gcc version.

[skmono]

Fixed with PR #42