Support Minisat source variants where l_False/l_True are not macros

[tautschnig]

There isn't really a single authoritative Minisat source anymore, and therefore system-provided Minisat installations may use slightly different source layouts. Cater for this by supporting at least the variants with/without macros for l_False/l_True.

Fixes: #8052

• 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 ✅

Comparison is base (3777fa9) 79.08% compared to head (c274d6e) 79.08%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8107      +/-   ##
===========================================
- Coverage    79.08%   79.08%   -0.01%     
===========================================
  Files         1698     1698              
  Lines       196491   196491              
===========================================
- Hits        155404   155401       -3     
- Misses       41087    41090       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.