[clang-tools-extra] Add --project-root to clangd (PR #155905)

[Aiden Grossman via cfe-commits]

boomanaiden154 wrote:

Seeing the same thing with ASan at -O1:
```
<<< initialize: {}
<-- initialize(0)
third_party/llvm/llvm-project/clang-tools-extra/clangd/ClangdLSPServer.cpp:557:14: runtime error: load of value 112, which is not a valid value for type 'bool'
```

Only `--gtest_filter="LSPTest*:GlobalCompilationDatabaseTest*"` is needed to reproduce this.

I've reverted this in 01c4eb5b9b0690692638e8be353e1c6cf2da5d9a.

https://github.com/llvm/llvm-project/pull/155905