C front-end: do not warn when re-initialising a variable with the same value

[tautschnig]

There is no surprising behaviour when all initialisers are the same.

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.39%. Comparing base (4a1a325) to head (e03011e).

Files with missing lines	Patch %	Lines
src/ansi-c/c_typecheck_base.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8695      +/-   ##
===========================================
- Coverage    80.40%   80.39%   -0.01%     
===========================================
  Files         1688     1688              
  Lines       207403   207400       -3     
  Branches        73       73              
===========================================
- Hits        166763   166745      -18     
- Misses       40640    40655      +15     

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[kroening]

Does the C standard guarantee that this works?

[tautschnig]

Does the C standard guarantee that this works?

The C standard would forbid a redefinition; yet we are seeing those in the C front-end as we (intentionally) do those redefinitions in our C model library. That said, the better fix might be to just no add (redundant zero-)initialisers in the model library. Will try.

[tautschnig]

Closing in favour of #8698.