goto-instrument/wmm: do not lookup non-existent symbols in the namespace

[tautschnig]

Making up function names on the spot resulted in failing namespace
lookups. Avoid those lookups altogether and pass in a known symbol. The
made-up name should instead be constructed via the suffix parameter,
which supports exactly this use case.

• 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

Merging #6102 (98f9cc2) into develop (4c14789) will increase coverage by 0.50%.
The diff coverage is 95.23%.

@@             Coverage Diff             @@
##           develop    #6102      +/-   ##
===========================================
+ Coverage    74.52%   75.03%   +0.50%     
===========================================
  Files         1447     1447              
  Lines       157808   157794      -14     
===========================================
+ Hits        117610   118397     +787     
+ Misses       40198    39397     -801     

Impacted Files	Coverage Δ
src/goto-instrument/wmm/shared_buffers.h	95.23% <75.00%> (+95.23%)	⬆️
src/goto-instrument/wmm/shared_buffers.cpp	77.83% <100.00%> (+77.83%)	⬆️
src/goto-programs/goto_program.h	91.63% <0.00%> (+0.64%)	⬆️
src/goto-instrument/wmm/cycle_collection.cpp	88.04% <0.00%> (+3.26%)	⬆️
src/goto-instrument/rw_set.h	47.27% <0.00%> (+5.45%)	⬆️
src/goto-instrument/wmm/event_graph.h	71.29% <0.00%> (+6.48%)	⬆️
src/goto-instrument/wmm/goto2graph.cpp	54.41% <0.00%> (+9.11%)	⬆️
src/goto-instrument/rw_set.cpp	52.68% <0.00%> (+10.75%)	⬆️
src/goto-instrument/wmm/goto2graph.h	92.85% <0.00%> (+11.90%)	⬆️
src/ansi-c/c_storage_spec.cpp	97.36% <0.00%> (+18.42%)	⬆️
... and 5 more

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[chrisr-diffblue]

Looks good to me! And apologies for the delay getting to review...