AthGeneration CMake Warning Fix, master branch (2021.12.10.)

Silenced the OpenMP messages emitted by FindBLAS.cmake to fix AGENE-2118.

This is a bit of a painful thing... CMake's FindBLAS.cmake module, when looking for a statically linked OpenBLAS library (which is what LCG provides...), also looks for OpenMP.

https://gitlab.kitware.com/cmake/cmake/-/blob/master/Modules/FindBLAS.cmake#L758-764

In a way that can really not be silenced in any convenient way. 😦 So I just brought out the big guns, silencing FindOpenMP through OpenMP_FIND_QUIETLY...