[clangd] Have suppression comments take precedence over warning-as-error

Summary: This matches the clang-tidy behaviour.

Fixes https://github.com/clangd/clangd/issues/375

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79691