[clang] [clang] Make verbose output streams configurable for embedded clients (PR #226022)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

Can we check how `[llvm::dbgs](https://llvm.org/doxygen/namespacellvm.html#a7c46c742c31be54870e2038048e6b391)` is done and possibly have `llvm::infos` which is by default wired to `llvm::errs()` and we can optionally rewire it to something else the user specified?

https://github.com/llvm/llvm-project/pull/226022