CMake openssl support

[wesm]

CMake built as is with the toolchain does not support HTTPS in ExternalProject_Add. I believe this can be fixed by setting --system-libs in the bootstrap call. See

https://github.com/conda-forge/cmake-feedstock/blob/master/recipe/build.sh

[wesm]

I checked locally that setting --system-curl is enough to solve the issue