Fix _Generic selection for pointer-to-array types

[tautschnig]

Use type compatibility matching instead of exact equality in _Generic. Also fix array type compatibility check to follow C11 6.2.7 standard: Arrays with unspecified size are compatible with specified sizes.

Fixes: #8690

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[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.93%. Comparing base (4fe3ade) to head (e0bc21c).

Files with missing lines	Patch %	Lines
src/ansi-c/c_typecheck_expr.cpp	91.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8749   +/-   ##
========================================
  Coverage    79.93%   79.93%           
========================================
  Files         1698     1698           
  Lines       187698   187705    +7     
  Branches        73       73           
========================================
+ Hits        150034   150043    +9     
+ Misses       37664    37662    -2     

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