Feature request

Edit: We have found an easy solution that does not require to generate a header file but works exclusively in CMake.
See #2012 and #2100.

Once these are reviewed, we can apply the logic to OCC and other external libs as well.

When a library links against t8code, they cannot access T8_ENABLE_OCC.
We should make these available in t8code header.
This is possible using cmake configure_file.

Is your feature request related to a problem? Please describe.
External libraries using t8code cannot see if t8code is linked against another library (for example OCC) and with which version of that library.

Describe the solution or feature you'd like
Create a header file with

T8_ENABLE_OCC // 0 or 1 depending on whether t8code is linked against OCCor not.
T8_OCC_MAJOR_VERSION // Defined only if T8_ENABLE_OCC  is true. The major version number of OCC that t8code links again.
T8_OCC_MINOR_VERSION // Defined only if T8_ENABLE_OCC  is true. The minor version number of OCC that t8code links again.  

Describe alternatives you've considered
N/A

Estimated priority

"Priority: medium" Should be solved within half a year

Additional context