Avoid conversion check failure sysconf library model

[tautschnig]

errno is signed. Also, fix test patterns and spelling mistakes in comments.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.05 🎉

Comparison is base (63b8b71) 78.13% compared to head (ecfc918) 78.18%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7824      +/-   ##
===========================================
+ Coverage    78.13%   78.18%   +0.05%     
===========================================
  Files         1698     1698              
  Lines       194027   194027              
===========================================
+ Hits        151600   151709     +109     
+ Misses       42427    42318     -109     

see 56 files with indirect coverage changes

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[feliperodri]

Thank you for the quick fix, @tautschnig!