Undefined shifts are now fatal

[kroening]

• 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

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.29%. Comparing base (621fe05) to head (c70148e).

Files	Patch %	Lines
src/ansi-c/goto-conversion/goto_check_c.cpp	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8304   +/-   ##
========================================
  Coverage    78.29%   78.29%           
========================================
  Files         1722     1722           
  Lines       188448   188448           
  Branches     18452    18452           
========================================
+ Hits        147540   147544    +4     
+ Misses       40908    40904    -4     

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[tautschnig]

Needs a rebase.