OSX/cmake: more work on T40887 and a tentative fix
- test fail due libiomp5 is not available @ testing time
- must solve this by adding requred flags/includes to tests
- atm release builds are possible with this hack
Install_deps: minor cleanup.

Patch D633 by simonrepp (Simon Repp), thx.
Fix T40986: crash on using the viewer node inside of group nodes.

Viewers were activated both inside the active group as well as the top
level tree (the latter being a quick fix for getting a fallback viewer).
This caused a race condition on the shared viewer image.

Now the active viewer is defined at node conversion time in the converter
so that only one can be active at a time without each node having to
follow complicated rules for exclusion.
Fix T40983 Particle Texture use of generated coordinates is wrong.

Particle texture eval was not taking the actual texture space for orco/
generated textures into account at all.
Fix T40785: "Select Grouped" Pass Index mode is redundant.
Revert "Object Select Similar tool now has a Pass Index option."

This reverts commit 7a6919a74eb08caaf21030c17fe7c2723394a3d6.
OSX/CMAKE: extend my former workaround for failing tests with clang-omp to all build types
- this workaround makes sure the breaking -fopenmp is not exposed to testcompiles which use C_FLAGS respective CXX_Flags
- -fopenmp is always added to the CMAKE_C(XX)_FLAGS_<BUILD_TYPE> now
- another way to solve this would be to move the Configure OpenMP part after all line 2366,
but i don’t know if this would be apreciated
OSX/CMAKE: Way better fix for T40887, checks where failing with clang-omp
- found a way to feed just extra flags to the testcompiles
Correct IS_EMPTY macro

also prevent reading from BM_ELEM_API_FLAG_ get/setters
WIP