TST: updated regression testing environments for HPC systems

[shanedsnyder]

• add entirely new regression test environments for OLCF Frontier and ALCF Polaris
  • Polaris slightly involved as had to develop new scripts based on PBS job scheduler
• remove NERSC Cori regression test environment as the system has been decommissioned
• renamed old cray-module-alcf -> cray-module-alcf-theta to clarify which system the environment is intended for
• modified NERSC Perlmutter and OLCF Crusher tests to use given Darshan install prefix rather than just using the default Darshan module provided by the system
• consolidate old README.CRAY.ALCF.txt and README.CRAY.NERSC.txt into a more general README.CRAY.txt file that describes how to run regression tests on Cray systems
• updated regression testing README to list newly added Cray regression testing environments

[shanedsnyder]

FWIW, regression testing is working and mostly passing on all HPC systems:

• ALCF Theta
• ALCF Polaris
• NERSC Perlmutter
• OLCF Crusher
• OLCF Frontier

The only notable exception is that our Fortran tests (fperf-f77/fperf-f90) are not generating Darshan logs on Polaris (these tests pass fine in all other Cray environments). I have not figured out what's happening, other than confirming Darshan is unable to intercept MPI_Init (which is key, obviously).

[shanedsnyder]

I eventually figured out the Polaris issue. We need to ensure we are using the GNU compilers when building Darshan there, as the default Nvidia compilers don't properly support "alias" attributes -- this prevents us from being able to intercept PMPI_ symbols which can be problematic for instrumenting some implementations of MPI fortran bindings.

Merging.