Partial fix for #13330 FN knownConditionTrueFalse with comma operator - #8965

AI review

I found no new problems. With if, else if, while, for and switch, the comma in the condition now gets a value in the cases the PR targets. Real function calls, constructor calls, template calls and lambda calls are still not given the comma value. I found no new false positives in loops, in do/while, or where the variable is changed through a pointer argument or a global inside the condition. As the title says, this is a partial fix. if (g(), n) where g is not pure and has no visible body is still not reported. The six differences in the 1000-package run all come from the (void)1,1 / (void)0,0 macro, which the author has already explained in comments.md.

Testing

• Built cppcheck and testrunner in pr/ and cppcheck in base/. All builds succeeded.
• ./testrunner TestCondition TestValueFlow passed. The full ./testrunner -q also passed: 5362 tests, 0 failures.
• I wrote scratch files and ran the PR binary on them, comparing with base where it mattered:
  • Newly reported with h() declared __attribute__((pure)), all correct:
    • if (h(), n), while (h(), n), else if (h(), n) and (h(), n) ? 1 : 2 give knownConditionTrueFalse.
    • if (n == 0) { if (h(), n == 0) {} } gives knownConditionTrueFalse.
    • switch (h(), n) { case 1: } gives unreachableSwitchCase.
    • if ((void)0, n) gives knownConditionTrueFalse.
  • Possible false positives, none reported:
    • while (h(), n < 10) { n++; }
    • do { n = k(0); } while (h(), n);
    • for (; h(), n < 3; n++)
    • if (h(), k(&n), n)
    • if (n = k(0), n)
    • x = 0; if (g(), x) where g sets the global x
  • Calls that should not get the comma value, unchanged from base:
    • S s(h(), n)
    • l(h(), n) where l is a lambda
    • t(h(), n) where t is a template
    • decltype(h(), n)(1) and sizeof(h(), n)
  • Still a false negative: if (h(), n) where h is a plain declaration with no body. This is the remaining part of #13330, as the "partial fix" title says.

Automated review of 2f62d59 by Claude. The pull request was built and tested locally.