[clangd] Add --query-driver flag to clangd-indexer

When using `clangd` for cross-compiled projects, it's necessary to use the `--query-driver` flag so that `clangd` can extract the compiler's built-in header paths. However, there's no such flag for `clangd-indexer` so we're unable to build a working static index for these projects.

This patch adds a `--query-driver` flag to `clangd-indexer` for this scenario.

I saw some tests under `clang-tools-extra/clangd/test/` but I think the cross-compilation case is a bit more complex to test. Let me know if you'd like me to look into this further.

Resolves: https://github.com/clangd/clangd/issues/1717

Reviewed By: nridge

Differential Revision: https://reviews.llvm.org/D157990