C library: implement {v,}dprintf

[tautschnig]

The model implementation has no side effects, but will make sure that the format string pointer can be dereferenced.

• 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 78.23%. Comparing base (c08e473) to head (6aeace1).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8238   +/-   ##
========================================
  Coverage    78.23%   78.23%           
========================================
  Files         1720     1720           
  Lines       188342   188342           
  Branches     18457    18442   -15     
========================================
  Hits        147353   147353           
  Misses       40989    40989           

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