Test __CPROVER_ID support in the C front-end

[tautschnig]

__CPROVER_ID permits constructing identifiers from strings that would not otherwise be valid identifier names in C. The test demonstrates one way of using this feature.

• 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.
• 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

Merging #7142 (2367b39) into develop (f20515f) will increase coverage by 0.00%.
The diff coverage is 75.00%.

@@           Coverage Diff            @@
##           develop    #7142   +/-   ##
========================================
  Coverage    77.86%   77.87%           
========================================
  Files         1576     1576           
  Lines       181805   181805           
========================================
+ Hits        141571   141578    +7     
+ Misses       40234    40227    -7     

Impacted Files	Coverage Δ
src/ansi-c/c_typecheck_expr.cpp	74.17% <ø> (ø)
src/ansi-c/parser.y	80.93% <ø> (+0.45%)	⬆️
src/goto-instrument/interrupt.cpp	0.00% <ø> (ø)
src/jsil/jsil_entry_point.cpp	0.00% <0.00%> (ø)
src/util/pointer_expr.h	80.83% <ø> (ø)
src/ansi-c/ansi_c_entry_point.cpp	89.45% <100.00%> (ø)
src/ansi-c/c_typecheck_base.cpp	82.50% <100.00%> (ø)

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