C front-end: fix processing of alignment and packing attributes

[tautschnig]

Packing needs to be evaluated as part of the definition of the type while alignment applies also when using a type. The position of the attribute also requires extra care as some positions are accepted by GCC (and warned about by Clang) while actually being ignored.

Fixes: #8443

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[codecov]

Codecov Report

Attention: Patch coverage is 78.72340% with 10 lines in your changes missing coverage. Please review.

Project coverage is 78.15%. Comparing base (2212cd6) to head (5eea045).

Files with missing lines	Patch %	Lines
src/ansi-c/parser.y	72.72%	6 Missing ⚠️
src/ansi-c/c_typecheck_type.cpp	84.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8454      +/-   ##
===========================================
- Coverage    78.38%   78.15%   -0.24%     
===========================================
  Files         1726     1726              
  Lines       188616   189216     +600     
  Branches     18295    18302       +7     
===========================================
+ Hits        147855   147889      +34     
- Misses       40761    41327     +566     

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