MOAR LOGGING

Context: #8681 (comment)

For some reason we see `crc641855b07eca6dcc03/GenericHolder_1.java`
in the log output, part of `@(_JavaStubFiles)`, but as far as we can
tell it *isn't* being compiled.

Which makes no sense.

My best conjecture is that `@(_JavaBindingSource)` doesn't include
everything within `@(_JavaStubFiles)`.

Update the `<Javac/>` task to print out the paths of all files that
at added to the response file, so that we can see what `javac`
is *actually* compiling.

src/Xamarin.Android.Build.Tasks/Tasks/JavaCompileToolTask.cs

@@ -63,8 +63,11 @@ private void GenerateResponseFile ()
 				WriteOptionsToResponseFile (sw);
 				// Include any user .java files
 				if (JavaSourceFiles != null)
-					foreach (var file in JavaSourceFiles.Where (p => Path.GetExtension (p.ItemSpec) == ".java"))
-						sw.WriteLine (string.Format ("\"{0}\"", file.ItemSpec.Replace (@"\", @"\\")));
+					foreach (var file in JavaSourceFiles.Where (p => Path.GetExtension (p.ItemSpec) == ".java")) {
+						var path    = file.ItemSpec.Replace (@"\", @"\\");
+						sw.WriteLine (string.Format ("\"{0}\"", path));
+						Log.LogDebugMessage ($"javac source: {path}");
+					}
 
 				if (string.IsNullOrEmpty (StubSourceDirectory))
 					return;
@@ -86,8 +89,10 @@ private void GenerateResponseFile ()
 					// Solution:
 					//    Since '\' is an escape character, we need to escape it.
 					// [0] http://download.oracle.com/javase/1.4.2/docs/api/java/io/StreamTokenizer.html#quoteChar(int)
+					var path    = file.Replace (@"\", @"\\").Normalize (NormalizationForm.FormC);
 					sw.WriteLine (string.Format ("\"{0}\"",
-								file.Replace (@"\", @"\\").Normalize (NormalizationForm.FormC)));
+								path));
+					Log.LogDebugMessage ($"javac source: {path}");
 				}
 			}
 		}