Fix va_list types for __CPROVER_OBJECT_SIZE in ARM64 Linux

[adpaco-aws]

In a nutshell, this is like #7521 but for __CPROVER_OBJECT_SIZE.
#7862 shows the compilation error I'm getting unless I apply the changes in this PR.

Fixes #7862

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• 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).
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[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.10% ⚠️

Comparison is base (d61bffc) 78.86% compared to head (9a0c662) 78.77%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7863      +/-   ##
===========================================
- Coverage    78.86%   78.77%   -0.10%     
===========================================
  Files         1699     1699              
  Lines       195229   195229              
===========================================
- Hits        153977   153794     -183     
- Misses       41252    41435     +183     

see 8 files with indirect coverage changes

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