[clangd] Log cc1 args at verbose level.

Summary: This will help debugging driver issues.

Reviewers: kbobyrev

Subscribers: ilya-biryukov, javed.absar, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D70832