Offline build

[hfiguiere]

Now it seems that RTNeural as built from BYOD 1.3, require to download something.

And if there is a way to disable it, I found nothing in the documentation.

(from BYOD 1.3.0)

-- RTNeural -- Using xsimd backend
CMake Error at modules/RTNeural/cmake/CPM.cmake:19 (file):
  file DOWNLOAD cannot compute hash on failed download

    status: [6;"Couldn't resolve host name"]
Call Stack (most recent call first):
  modules/RTNeural/CMakeLists.txt:9 (include)

Building offline is essential in making sure the builds a reproducible.