Update hh.mod for CoreNEURON compatibility changes hh.mod in place during build

[mgeplf]

Context

Overview of the issue

When CoreNEURON is enabled in build, the hh.mod file gets updated in place, which means it's easy to check it in by accident.

Expected result/behavior

If changes to mod files are needed, the should probably be done in a separate directly that isn't tracked by source control.

NEURON setup

• Version: master branch

Minimal working example - MWE

• CMake build commands:

mkdir build && cd build
cmake -DNRN_ENABLE_CORENEURON=ON  ..
cmake --build . --

[mgeplf]

This is directed by this:
https://github.com/neuronsimulator/nrn/blob/master/CMakeLists.txt#L747

Not sure what the best course of action is.

[JCGoran]

Could the mod files first be copied to some temp dir, and then compiled? IIRC, nrnivmodl doesn't care where the mod files themselves are, since the compiled files will be placed in $PWD/<arch> anyway.

[mgeplf]

I haven't looked too deaply at it, but I think that's true.