[clang] [clang-tools-extra] [clang-tidy] [Modules] Skip checking decls in clang-tidy (PR #145630)

[Baranov Victor via cfe-commits]

vbvictor wrote:

This must be the same as in https://github.com/llvm/llvm-project/pull/178471
Instead of using raw `clang`, we should use `%clang` from lit cfg. 
This brings dependency of clang to CLANG_TOOLS_TEST_DEPS which hasn't landed yet.
I think at the time my expectance was that we already had `clang`, but apparently we don't.

https://github.com/llvm/llvm-project/pull/145630