[clang] NFCI: Use DirectoryEntryRef in collectIncludePCH

This patch removes use of the deprecated `DirectoryEntry::getName()` from `collectIncludePCH` by using `{File,Directory}EntryRef` instead.

Reviewed By: bnbarham

Differential Revision: https://reviews.llvm.org/D123769

clang/lib/Frontend/CompilerInstance.cpp

@@ -232,15 +232,15 @@ static void collectIncludePCH(CompilerInstance &CI,
 
   StringRef PCHInclude = PPOpts.ImplicitPCHInclude;
   FileManager &FileMgr = CI.getFileManager();
-  auto PCHDir = FileMgr.getDirectory(PCHInclude);
+  auto PCHDir = FileMgr.getOptionalDirectoryRef(PCHInclude);
   if (!PCHDir) {
     MDC->addFile(PCHInclude);
     return;
   }
 
   std::error_code EC;
   SmallString<128> DirNative;
-  llvm::sys::path::native((*PCHDir)->getName(), DirNative);
+  llvm::sys::path::native(PCHDir->getName(), DirNative);
   llvm::vfs::FileSystem &FS = FileMgr.getVirtualFileSystem();
   SimpleASTReaderListener Validator(CI.getPreprocessor());
   for (llvm::vfs::directory_iterator Dir = FS.dir_begin(DirNative, EC), DirEnd;