[SPI-2465] Add 104c_ATLAS_3/4
Includes LCG_104c_ATLAS_3/4 with:
- Pythia308
- installation of MCFM and Sherpa 2.2.14p1 (+ MPI-enabled Sherpa) with the additional —enable-mcfm flag.
- GRPC
- madgraph5amc 3.5.2 with patches reviewed and updated by Zach Marshall
- apfel 3.1.0 with new CMake build system.
Edited by Dmitri Konstantinov