[clang-tools-extra] [clang-tidy] add depercation warning for non-whitelisted global options (PR #121057)

[Carlos Galvez via cfe-commits]

carlosgalvezp wrote:

> that it is kept for future deprecations (and would therefore need to be general enough)

Yes, that was my thought, some general-purpose mechanism for deprecation warnings, for example `--disable-deprecation-warnings`, `--no-deprecation-warnings`, etc.

The use case I have in mind is when e.g. a 3rd-party .cpp file is pulled in via the compilation database, normally it will be analyzed via its own .clang-tidy file that normally one doesn't have control over. One could however argue that one should probably only analyze own source files, not 3rd-party ones. One probably also doesn't want to disable deprecation warnings globally just because a 3rd-party triggers them - it'd be better to filter out such 3rd-party code from analysis.

Perhaps we can just land this as is for now and introduce the escape hatch if we get feedback indicating it's needed?

https://github.com/llvm/llvm-project/pull/121057