c compiler availability in environments

[yunlongxu-numagic]

currently we hard-code to use gcc to compile casadi backend, this might be problematic.

• in our conda workflow, we didn't install gcc manually, but it was available (unit tests passed). It uses ubuntu-latex os
• in docker env, we install gcc manually, from ubuntu OS

If there is a need to manually install the compiler in the environment, then we might also need to think about OS dependent options. Maybe we want to use clang for MacOS env. (weirdly, with conda test on MacOS, currently gcc is also available by default!)