[clangd] Disable background-index on lit-tests by default
[clangd] Disable background-index on lit-tests by default

Summary:
Since background-index can perform disk writes, we don't want to turn
it on tests that won't clear it.

Reviewers: sammccall

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64990

git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@366575 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra