Kokkos CUDA failes to compile with OMPI_CXX and MPICH_CXX wrappers

[stanmoore1]

LAMMPS uses the OMPI_CXX and MPICH_CXX wrappers, see below. However, this functionality was broken due to recent changes in Makefile.kokkos.

export OMPI_CXX = $(KOKKOS_PATH)/config/nvcc_wrapper
CC =            mpicxx

See PR #775 for a fix.

[stanmoore1]

The issue is that when using OMPI_CXX the nvcc compiler isn't found, and I get errors like:

g++: error: =sm_35: No such file or directory

[stanmoore1]

This was broken by b586204.

[crtrott]

We triaged the problem. There is a real issue with the root cause being that you can't seem to be able to set environment variables for commands run in the shell inside of Make. This means if you try to set OMPI_CXX inside of the Makefile it will be honored for the actual compilation, but some of our "What compiler I am using" logic doesn't see that setting. The associated pull request works around the issue in a sane way for now, but we need to be aware that it doesn't fix the root issue.

[nmhamster]

@dsunder - I found this on the GNU make documentation. I think it may be useful for you: https://www.gnu.org/software/make/manual/make.html#Execution