Contracts: always remove spurious do {... } while(0) loops

[tautschnig]

None of our contracts instrumentation should spuriously get confused by these pseudo-loops (suggesting to users that they need to unwind those loops). We already used to do this for non-DFCC code, now also apply it with dynamic frames.

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• 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).
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.38%. Comparing base (5002f3b) to head (d4afdd2).
Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8459      +/-   ##
===========================================
+ Coverage    78.35%   78.38%   +0.03%     
===========================================
  Files         1726     1726              
  Lines       188695   188612      -83     
  Branches     18301    18264      -37     
===========================================
  Hits        147851   147851              
+ Misses       40844    40761      -83     

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