Add error message on support lib build failure

Change-Id: I7df35e878b3310c7d6f158911f81aa21557f1032
diff --git a/build.gradle b/build.gradle
index 6a90344..5181fbd 100644
--- a/build.gradle
+++ b/build.gradle
@@ -170,6 +170,17 @@
     }
 }
 
+project.gradle.buildFinished { buildResult ->
+    if (buildResult.getFailure() != null) {
+        println()
+        println 'Build failed. Possible causes include:'
+        println '    1) Bad codes'
+        println '    2) Out of date prebuilts in prebuilts/sdk'
+        println '    3) Need to update the compileSdkVersion in a library's build.gradle'
+        println()
+    }
+}
+
 FileCollection getAndroidPrebuilt(String apiLevel) {
     files("$rootDir/../../prebuilts/sdk/$apiLevel/android.jar")
 }