[clang][CodeGen] NFCI: Use FileEntryRef

[jansvoboda11]

Summary

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

clang/lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::CreateCompileUnit() {
   if (MainFileName.empty())
     MainFileName = "<stdin>";
 
   // The main file name provided via the "-main-file-name" option contains just
   // the file name itself with no path information. This file name may have had
   // a relative path, so we look into the actual file entry for the main
   // file to determine the real absolute path for the file.
   std::string MainFileDir;
-  if (const FileEntry *MainFile = SM.getFileEntryForID(SM.getMainFileID())) {
-    MainFileDir = std::string(MainFile->getDir()->getName());
+  if (Optional<FileEntryRef> MainFile =
+          SM.getFileEntryRefForID(SM.getMainFileID())) {
+    MainFileDir = std::string(MainFile->getDir().getName());
     if (!llvm::sys::path::is_absolute(MainFileName)) {
       llvm::SmallString<1024> MainFileDirSS(MainFileDir);
       llvm::sys::path::append(MainFileDirSS, MainFileName);
       MainFileName =
           std::string(llvm::sys::path::remove_leading_dotslash(MainFileDirSS));
     }
     // If the main file name provided is identical to the input file name, and
     // if the input file is a preprocessed source, use the module name for

clang/lib/CodeGen/CGObjCGNU.cpp

llvm::Constant *module = [&] {
     auto module = builder.beginStruct(moduleTy);
     // Runtime version, used for ABI compatibility checking.
     module.addInt(LongTy, RuntimeVersion);
     // sizeof(ModuleTy)
     module.addInt(LongTy, CGM.getDataLayout().getTypeStoreSize(moduleTy));
 
     // The path to the source file where this module was declared
     SourceManager &SM = CGM.getContext().getSourceManager();
-    const FileEntry *mainFile = SM.getFileEntryForID(SM.getMainFileID());
+    Optional<FileEntryRef> mainFile =
+        SM.getFileEntryRefForID(SM.getMainFileID());
     std::string path =
-      (Twine(mainFile->getDir()->getName()) + "/" + mainFile->getName()).str();
+        (mainFile->getDir().getName() + "/" + mainFile->getName()).str();
     module.add(MakeConstantString(path, ".objc_source_file_name"));
     module.add(symtab);
 
     if (RuntimeVersion >= 10) {
       switch (CGM.getLangOpts().getGC()) {
       case LangOptions::GCOnly:
         module.addInt(IntTy, 2);
         break;