* Modify Flang NVidia GPU variant to make use of built-in CudaPackage
* Add OpenMP Offload patch if March 2019 compiler is selected.
* Flang parallel build has a race condition.
* llvm-flang now uses built-in CudaPackage.
* Add variant for different build releases.
* Fix OpenMP target offload for NVidia GPUs.
* Additional commong flags that are needed with comments.
* NVidia BC required for libomp target requires special treatment. Use clang built in previous step to re-compile libomptarget.
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