Use of ifx in intel toolchains

[hattom]

Since oneAPI, Intel ships 2 sets of compilers: Classic: icc, icpc, ifort, and LLVM-based: icx, icpx, ifx.

Unlike icx and icpx, ifx is barely production-ready, still lagging behind ifort (it's finally out of beta, but that was not so long ago).

Two issues stand-out:

1. MPI: mpiifort -fc=ifx is the correct MPI command according to [1]
2. compatibility: presumably, fortran .mod files are not compatible between ifort and ifx. If this is indeed the case, does a separate toolchain make more sense than having a toolchain option?

(Related to https://github.com/easybuilders/easybuild-framework/issues/4009, but specifically relates to Fortran matters).

[1] https://www.intel.com/content/www/us/en/develop/documentation/mpi-developer-reference-linux/top/command-reference/compiler-commands/compilation-command-options.html

[hattom]

"2." seems to not be a problem, .mod files seem compatible.

[hattom]

For "1.", https://github.com/easybuilders/easybuild-framework/pull/4032/files should probably be updated, also for the mpi equivalents of icx and icpx: mpiicc -cc=icx and mpiicpc -cxx=icpx (assuming not DPC++).

[hattom]

We can close. As @boegel pointed out on #4062, , this is already handled by env variables.