[mlir] Add error message when failing to add pass

[jpienaar]

Summary

Ran into failure without any error message previously here.

[mehdi_amini]

Is this easily testable?

[jpienaar]

Add simple test

mlir/lib/Pass/PassRegistry.cpp

 }
 
 /// Add the given pipeline elements to the provided pass manager.
 LogicalResult TextualPipeline::addToPipeline(
     ArrayRef<PipelineElement> elements, OpPassManager &pm,
     function_ref<LogicalResult(const Twine &)> errorHandler) const {
   for (auto &elt : elements) {
     if (elt.registryEntry) {
-      if (failed(
-              elt.registryEntry->addToPipeline(pm, elt.options, errorHandler)))
-        return failure();
+      if (failed(elt.registryEntry->addToPipeline(pm, elt.options,
+                                                  errorHandler))) {
+        return errorHandler("failed to add `" + elt.name + "` with options `" +
+                            elt.options + "`");
+      }
     } else if (failed(addToPipeline(elt.innerPipeline, pm.nest(elt.name),
                                     errorHandler))) {
-      return failure();
+      return errorHandler("failed to add `" + elt.name + "` with options `" +
+                          elt.options + "` to inner pipeline");
     }
   }
   return success();
 }
 
 /// This function parses the textual representation of a pass pipeline, and adds
 /// the result to 'pm' on success. This function returns failure if the given
 /// pipeline was invalid. 'errorStream' is an optional parameter that, if