[clangd] exclude check-clangd from check-all, fix buildbot failure. check-clangd is included via check-clang-tools, otherwise we will run two instances of check-clangd in parallel when running 'check-all', which may have race condition. llvm-svn: 343526 GitOrigin-RevId: 3e0c1bdbe41c980950cb0041d34cafbd967c2e3d