[clangd] system headers not found for yocto builds

i'm using qtcreator for cross-compiling a yocto-based project. setting up the cross toolchain is working nicely these days by setting `CMAKE_TOOLCHAIN_FILE` to `usr/share/cmake/Qt6Toolchain.cmake` inside my yocto sdk.

however clangd doesn't find the system headers. without having a closer look, it seems that clangd has a --query-driver argument that can be used for this use cases. makes me wonder if we can convince qtcreator to set this argument, derive the value from the CMAKE_CXX_COMPILER value (pointing to the cross compiler)