Add support for GNU Hurd

[tautschnig]

Builds with tests passing on hurd-i386 per https://buildd.debian.org/status/fetch.php?pkg=cbmc&arch=hurd-i386&ver=5.95.1-6&stamp=1714528231&raw=0.

• 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

All modified and coverable lines are covered by tests ✅

Project coverage is 78.32%. Comparing base (905033e) to head (6950014).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8211      +/-   ##
===========================================
- Coverage    78.32%   78.32%   -0.01%     
===========================================
  Files         1721     1721              
  Lines       188210   188219       +9     
  Branches     18462    18533      +71     
===========================================
  Hits        147416   147416              
- Misses       40794    40803       +9     

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