Fix compiler warnings, second try

[PhilMiller]

My previous PR #47 didn't get the flags right to actually match intentions, so the code changes to satisfy CI in that PR were incomplete. This PR fixes the flags to enforce our expectation of no compiler warnings, and fixes the code accordingly.

Changes

• Fix variable name in CMake arguments in CI
• Add -Og so that the compiler does analysis necessary to see that fgets() and fscanf() return values were unchecked
• Check said return values, and report errors up the call stack through to BMI_FAILURE

Testing

1. CI

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
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Testing checklist

Target Environment support

• Linux/GCC9 (Ubuntu 20.04)
• macOS with AppleClang

[aaraney]

Thanks for making these improvements, @PhilMiller!

[aaraney]

Neat! I wasn't aware of this flag.