[clang-tools-extra] [clang-tidy] New checker: modernize-use-va-opt to replace the `, ##__VAR_ARG__` GNU extension (PR #188474)

[via cfe-commits]

serge-sans-paille wrote:

For reviewers: although I wrote `__VA_OPT__(,)` in the FixIt replacement, and although the fixit is correctly printed, it's applied as `__VA_OPT__()` instead, eating the comma. Is that a known issue?

https://github.com/llvm/llvm-project/pull/188474