[C/C++] Unittests with googletest

mentioned in merge request !5 (closed)

@b382190 Could you make this set of tests more complete once you are back from holiday?

just my 2cts: IMO the C-part of libfortran-support is minimal compared to the rest. using googletest for that part is reasonable, but for the fortran code it seems like an overkill.

This approach is more like a feasibility study, but I would be regard it for a production solution.

Isn't there a simpler pure-fortran solution for this?

For a more complete set of Fortran unittest please have a look at !13 (merged) .

The idea is that C/C++ test are in googletest. Also we might want to test some of the fortran-wrappers of C-function and compare directly to results from the C-function -> there we need googletest.

The test present in this MR were part of our investigation about unittest possibilities. It needs a consolidation and cleanup, but also more tests for the C/C++ parts.

This should be done by @b382190 once he is back from holiday.

Some small comments

deleted the cmake_for_tests branch. This merge request now targets the master branch

added 1 commit

f17a796a - Add macro for c tests

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c7b21da9 - Set macro for all google tests

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added 3 commits

c0b2cb7c - Avoid unresolved symbols on macOS
13c32569 - Resolve unused signal code for MAC OS
aa2336d8 - Merge remote-tracking branch 'origin/fix-unresolved-symbols-macos' into c_c++_tests

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