Add CI with CMake

[wenzeslaus]

@rkanavath I'm opening this as a PR against the branch in your repo. I did a rebase to the latest master, so there is a lot of changes comparing to your branch. If you rebase to master and force push to yours, this will show a proper diff. I can also force push to your branch if you are fine with that. Please, let me know.

This adds CI, but does not change any code. It is basically what was here, but now it is natively part of the code and will be visible in the PR.

You don't have GitHub Actions enabled, but you can see the tests running in my fork. Like before, the build runs, but grass executable (grass79, grass.py, ...) is not in the right place, so tests fail.

[rkanavath]

can you sync with master so that only relavant changes are shown, then i can merge it
I

[wenzeslaus]

The CMake build fails with:

Scanning dependencies of target v.neighbors
[ 73%] Building C object vector/CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o
[ 73%] Building C object raster3d/r3.flow/CMakeFiles/test.r3flow.dir/interpolate.c.o
[ 73%] Building C object raster3d/r3.flow/CMakeFiles/test.r3flow.dir/voxel_traversal.c.o
[ 73%] Linking C executable ../../bin/test.r3flow
[ 73%] Linking C executable ../bin/v.neighbors
Creating /home/runner/work/grass/grass/build/gisbase/docs/html/test.r3flow.html
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x0): undefined reference to `c_count'
vector/CMakeFiles/v.neighbors.dir/build.make:129: recipe for target 'bin/v.neighbors' failed
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x20): undefined reference to `c_sum'
CMakeFiles/Makefile2:18241: recipe for target 'vector/CMakeFiles/v.neighbors.dir/all' failed
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x40): undefined reference to `c_ave'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x60): undefined reference to `c_median'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x80): undefined reference to `c_mode'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0xa0): undefined reference to `c_min'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0xc0): undefined reference to `c_max'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0xe0): undefined reference to `c_range'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x100): undefined reference to `c_stddev'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x120): undefined reference to `c_var'
CMakeFiles/v.neighbors.dir/v.neighbors/main.c.o:(.data.rel+0x140): undefined reference to `c_divr'
collect2: error: ld returned 1 exit status
make[2]: *** [bin/v.neighbors] Error 1
make[1]: *** [vector/CMakeFiles/v.neighbors.dir/all] Error 2

But the other builds run fine and that was the whole point of this PR - to bring the tests from master here and to add CMake build with tests to CI. Both are done, so I suggest to merge this to your branch now and to continue in OSGeo#348. As for merging, I suggest Rebase and merge here to have the individual commits for review if needed, but I have no strong opinion on that (we'll Squash and merge in the main repo anyway).