[clangd] Preserve -nostdinc and --sysroot when calling query driver

Solves this issue: https://github.com/clangd/clangd/issues/157

This is my first contribution to an llvm project, so I hope I'm doing it right!

Patch by @topisani (Tobias Pisani)!

Reviewers: kadircet, klimek

Differential Revision: https://reviews.llvm.org/D73811