Adds pthreads dependency for UnitsHelper

[mattw-nws]

Adds explicit dependency on threading for unit conversion (in core_mediator library). This eliminates "Unknown error -1" messages from the unit conversion code and makes output match between builds with no MPI or Python enabled and builds with MPI or Python (or both) enabled. (Enabling Python or MPI causes pthreads to be linked implicitly.) Without this, all unit conversion fails if ngen is built without Python or MPI, which resulted in a mismatch in output between builds without Python/MPI and builds with either.

Additions

• Added CMakeLists directives to require pthreads

Removals

Changes

Testing

1. Manual tests on builds without Python or MPI, checking/comparing output with Python/MPI enabled builds. (Notably: GoogleTest builds with pthreads, so the automated tests pass without this fix!)

2. Checking binary dependencies with ldd

Screenshots

Notes

Todos

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Testing checklist (automated report can be put here)

Target Environment support

• Linux

[stcui007]

I have tested this bug fix on Sugar Creek, HUC01, and a small artificial hydrofabric. They all give consistent results between the serial run and parallel runs with a number of chosen CPU cores: 8, 16, 32, 64, 96. So it looks like this fixes the issue encountered.

[stcui007]

Has left a comment.