Merging r368549:

------------------------------------------------------------------------
r368549 | hokein | 2019-08-12 11:35:04 +0200 (Mon, 12 Aug 2019) | 11 lines

[clangd] Drop diags from non-written #include.

Summary: This would fix that we show weird diagnostics on random lines of the main file.

Reviewers: ilya-biryukov

Subscribers: MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66074
------------------------------------------------------------------------

llvm-svn: 368683