v5.0.x: gcc 14 and clang 18 compiler warning fixes

[jsquyres]

This is a partial cherry pick from main PR #12743 (only 4 out of the 9 commits from #12743 apply to the v5.0.x branch).

See individual commit messages for details.

[wenduwan]

CI failure is runtime related.

Run mpiexec -n 3 python test/main.py -v -f
--------------------------------------------------------------------------
There are not enough slots available in the system to satisfy the 3
slots that were requested by the application:

  python

Either request fewer procs for your application, or make more slots
available for use.

A "slot" is the PRRTE term for an allocatable unit where we can
launch a process.  The number of slots available are defined by the
environment in which PRRTE processes are run:

  1. Hostfile, via "slots=N" clauses (N defaults to number of
     processor cores if not provided)
  2. The --host command line parameter, via a ":N" suffix on the
     hostname (N defaults to 1 if not provided)
  3. Resource manager (e.g., SLURM, PBS/Torque, LSF, etc.)
  4. If none of a hostfile, the --host command line parameter, or an
     RM is present, PRRTE defaults to the number of processor cores

In all the above cases, if you want PRRTE to default to the number
of hardware threads instead of the number of processor cores, use the
--use-hwthread-cpus option.

Alternatively, you can use the --map-by :OVERSUBSCRIBE option to ignore the
number of available slots when deciding the number of processes to
launch.
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