Allow dynamic loading of slurm_conf on Anvil.

[joaander]

Description

Set the RTLD_NOW and RTLD_GLOBAL ldopen flags.

Motivation and context

After a recent update on Purdue Anvil, HOOMD-blue fails to import with the error /usr/lib64/slurm/auth_munge.so: undefined symbol: slurm_conf.

From what I can tell, this is due to compile-time options for SLURM on Anvil which are outside our control:

• slurm sstat command, munge undefined symbol  NVIDIA/deepops#720 (comment)
• Default to building Slurm with dynamic libs NVIDIA/deepops#1021

Setting RTLD_GLOBAL may cause segfaults, so I limit this setting to only Anvil. Should users report problems on Anvil, we can investigate other options.

How has this been tested?

I executed hoomd-benchmarks on Anvil.

Change log

Fixed:

* Prevent ``/usr/lib64/slurm/auth_munge.so: undefined symbol: slurm_conf`` error on Purdue Anvil
  (`#1850 <https://github.com/glotzerlab/hoomd-blue/pull/1850>`__).

Checklist:

• I have reviewed the Contributor Guidelines.
• I agree with the terms of the HOOMD-blue Contributor Agreement.
• My name is on the list of contributors (sphinx-doc/credits.rst) in the pull request source branch.