[clangd] Initial clang-tidy diagnostics support.
Summary:
This runs checks over a restricted subset of the TU:
- preprocessor callbacks just receive the truncated PP events that
occur when a preamble is used.
- ASTMatchers run only over the top-level decls in the main-file
This patch just turns on one simple check (bugprone-sizeof-expression)
with no configuration. Configuration is complex enough to warrant a separate patch
This depends on a patch allowing traversal to be restricted to a scope.
Reviewers: hokein
Subscribers: srhines, mgorny, ilya-biryukov, ioeric, MaskRay, jkorous, arphaman, kadircet, cfe-commits
Differential Revision: https://reviews.llvm.org/D54204
llvm-svn: 347036