Byte-operator lowering: struct and union constants are not ID_constant

[tautschnig]

These are struct- and union expressions, or possible empty_union_exprt. Creating constant_exprt resulted in a segmentation fault in simplifying member expressions, as witnessed when working on
model-checking/kani#705.

• 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

Base: 78.29% // Head: 78.31% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (54369a6) compared to base (fb99063).
Patch coverage: 93.75% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7352      +/-   ##
===========================================
+ Coverage    78.29%   78.31%   +0.02%     
===========================================
  Files         1642     1644       +2     
  Lines       190023   190206     +183     
===========================================
+ Hits        148769   148959     +190     
+ Misses       41254    41247       -7     

Impacted Files	Coverage Δ
src/solvers/smt2_incremental/object_tracking.h	100.00% <ø> (ø)
..._incremental/smt2_incremental_decision_procedure.h	75.00% <ø> (ø)
src/util/lower_byte_operators.cpp	92.62% <28.57%> (-0.09%)	⬇️
...c/goto-programs/ensure_one_backedge_per_target.cpp	84.09% <82.97%> (-1.63%)	⬇️
...t/solvers/smt2_incremental/convert_expr_to_smt.cpp	99.60% <94.73%> (-0.10%)	⬇️
src/solvers/smt2/smt2_conv.cpp	66.97% <95.83%> (+0.18%)	⬆️
src/goto-programs/builtin_functions.cpp	58.95% <100.00%> (+0.43%)	⬆️
src/goto-programs/remove_returns.cpp	98.15% <100.00%> (ø)
src/goto-symex/symex_clean_expr.cpp	93.16% <100.00%> (ø)
src/goto-symex/symex_dereference.cpp	89.89% <100.00%> (+0.10%)	⬆️
... and 13 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.