Add sanitizer headers for provided clangd

Running clangd in QtCreator gives me warnings about missing headers:

```
In included file: 'sanitizer/asan_interface.h' file not found
```

This could be fixed by adding the headers from my local llvm installation to the "libexec" clangd directory.
Could this headers provided with an standard installation of clang cause building with sanitizers gets more and more popular?
Or could this issue be solved in an other way?