locateMacro doesn't respect the language options

In the [`locateMacro`](https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/include-cleaner/lib/LocateSymbol.cpp#L59), we call `tooling::stdlib::Symbol::named("", M.Name->getName())` without providing the a `Lang` argument (by default, it is C++). It is wrong if the analysis file is a C file.