[clang-tools-extra] [clang-tidy] Check for `-ignore-insert-conflict` support before using it in `apply_fixes` in `run-clang-tidy.py` (PR #127066)

[Vicente Mataix Ferrándiz via cfe-commits]

loumalouomega wrote:

> I am a bit confused here. If you're using the **system** Clang toolchain assembled by your company (outside of your control), that toolchain should have delivered a `run-clang-tidy.py` that is appropriate for that version.
> 
> If you are using `run-clang-tidy.py` from the Git working directory obtained from upstream sources (i.e., `run-clang-tidy.py` is newer and has this flag), then all the other tools (including `clang-tidy` and `clang-apply-replacements`) should be the appropriate newer version.
> 
> Otherwise you might be mixing versions, standard library implementations, intrinsic headers, etc., and there will be plenty of subtle bugs lurking behind every corner!
> 
> So in general, what was the original point you're trying to achieve? To me, the solution to the lack of `-ignore-insert-conflict` in `clang-apply-replacements` would be to **build a newer `clang-apply-replacements`** and have that in the _`PATH`_ earlier than the system version. So your local `clang-tidy` binary, the `clang-apply-replacements`, and the `run-clang-tidy.py` are all appropriately from the same version.

I have a certain version of Ubuntu with a certain version of Clang, not custom compiled.

https://github.com/llvm/llvm-project/pull/127066