[clangd] Make background index less chatty

[ilya-biryukov]

Summary

It is producing too much input in non-verbose mode,
i.e. a message per indexed file

clang-tools-extra/trunk/clangd/index/Background.cpp

llvm::Error BackgroundIndex::index(tooling::CompileCommand Cmd,
 
   // Take a snapshot of the digests to avoid locking for each file in the TU.
   llvm::StringMap<FileDigest> DigestsSnapshot;
   {
     std::lock_guard<std::mutex> Lock(DigestsMu);
     DigestsSnapshot = IndexedFileDigests;
   }
 
-  log("Indexing {0} (digest:={1})", Cmd.Filename, llvm::toHex(Hash));
+  vlog("Indexing {0} (digest:={1})", Cmd.Filename, llvm::toHex(Hash));
   ParseInputs Inputs;
   Inputs.FS = std::move(FS);
   Inputs.FS->setCurrentWorkingDirectory(Cmd.Directory);
   Inputs.CompileCommand = std::move(Cmd);
   auto CI = buildCompilerInvocation(Inputs);
   if (!CI)
     return llvm::createStringError(llvm::inconvertibleErrorCode(),
                                    "Couldn't build compiler invocation");