FindMPI: Deny -fexceptions from NVCC

Do not forward -fexceptions (set from MVAPICH2) to NVCC.

Needed for MVAPICH2 with NVCC when using CUDA as first-class CMake language. (Seems to be no problem with legacy FindCUDA.cmake)

Fixes: #18558 (closed)
Backport: release
Topic-rename: FindMPI-nvcc-fexceptions