[clangd] Query driver reads stderr and passes driver as first argument

Summary:
gcc invokes cc1 through a path deduced from argv[0] therefore it must
be correctly set.
Also it prints the search path to stderr not stdout, this also applies to clang.

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64196

llvm-svn: 365132