[clang] [TEST-ONLY] Make sure clang-extdef-mapping don't infer database (PR #195196)

[Steven Wu via cfe-commits]

cachemeifyoucan wrote:

> > I don't have better idea. We can change the substitution to pass an argument for not searching database maybe?
> 
> What do you mean by the "argument"? I'm afraid, I don't have the context.

You can implement a `clang-extdef-mapping -no-compilation-database-search` option that disable the search. Then `%clang_extdef_map` can be expanded to `clang-extdef-mapping -no-compilation-database-search` and make sure all tests are using the substitution instead of calling the tool directly.

https://github.com/llvm/llvm-project/pull/195196