llvm-reduce: Report file opening errors

This was also trying to write the bitcode to the failed file
on failure, which asserts. Also, consistently use
ToolOutputFile, instead of one path manually removing
the temp file.

llvm/tools/llvm-reduce/deltas/Delta.cpp

@@ -79,24 +79,17 @@ bool isReduced(ReducerWorkItem &M, TestRunner &Test) {
     exit(1);
   }
 
-  if (TmpFilesAsBitcode) {
-    llvm::raw_fd_ostream OutStream(FD, true);
-    writeBitcode(M, OutStream);
-    OutStream.close();
-    if (OutStream.has_error()) {
-      errs() << "Error emitting bitcode to file '" << CurrentFilepath << "'!\n";
-      sys::fs::remove(CurrentFilepath);
-      exit(1);
-    }
-    bool Res = Test.run(CurrentFilepath);
-    sys::fs::remove(CurrentFilepath);
-    return Res;
-  }
   ToolOutputFile Out(CurrentFilepath, FD);
-  M.print(Out.os(), /*AnnotationWriter=*/nullptr);
+
+  if (TmpFilesAsBitcode)
+    writeBitcode(M, Out.os());
+  else
+    M.print(Out.os(), /*AnnotationWriter=*/nullptr);
+
   Out.os().close();
   if (Out.os().has_error()) {
-    errs() << "Error emitting bitcode to file '" << CurrentFilepath << "'!\n";
+    errs() << "Error emitting bitcode to file '" << CurrentFilepath
+           << "': " << Out.os().error().message();
     exit(1);
   }