[FileSystemStatCache] Update test for new FileSystemStatCache API

[harlanhaskins]

Summary

Update this test to return std::error_code instead of LookupResult.

[arphaman]

LG

unittests/Basic/FileManagerTest.cpp

public:
   }
 
   // Inject a directory with the given inode value to the fake file system.
   void InjectDirectory(const char *Path, ino_t INode) {
     InjectFileOrDirectory(Path, INode, /*IsFile=*/false);
   }
 
   // Implement FileSystemStatCache::getStat().
-  LookupResult getStat(StringRef Path, llvm::vfs::Status &Status, bool isFile,
+  std::error_code getStat(StringRef Path, llvm::vfs::Status &Status,
+                          bool isFile,
                           std::unique_ptr<llvm::vfs::File> *F,
                           llvm::vfs::FileSystem &FS) override {
 #ifndef _WIN32
     SmallString<128> NormalizedPath(Path);
     llvm::sys::path::native(NormalizedPath);
     Path = NormalizedPath.c_str();
 #endif
 
     if (StatCalls.count(Path) != 0) {
       Status = StatCalls[Path];
-      return CacheExists;
+      return std::error_code();
     }
 
-    return CacheMissing;  // This means the file/directory doesn't exist.
+    return std::make_error_code(std::errc::no_such_file_or_directory);
   }
 };
 
 // The test fixture.
 class FileManagerTest : public ::testing::Test {
  protected:
   FileManagerTest() : manager(options) {
   }