[clangd] Fix flag name from r318327
[clangd] Fix flag name from r318327

git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@318329 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