[benchmark] Add a note that states if we failed to find the swift benchmark suite.

This will make it easier to identify in the CI if we failed to find the swift
benchmark suite.

Author: gottesmm

lit.cfg

@@ -163,7 +163,9 @@ if os.path.exists(swift_benchmarks_path):
     config.available_features.add("have-swift-benchmarks")
     config.substitutions.append( ('%{swift_benchmarks_path}', swift_benchmarks_path) )
     lit_config.note('testing using swift benchmarks at path: {}'.format(swift_benchmarks_path))
-    
+else:
+    lit_config.note('Failed to find swift benchmarks, skipping related tests.')
+
 # Find the tools we need.
 
 swift_path = lit_config.params.get(