Fail on warnings with compileGroovy (since it compiles Java code as well)

(cherry picked from commit d77ecb26a9)

spring-beans/spring-beans.gradle

@@ -21,6 +21,7 @@ sourceSets {
 compileGroovy {
 	sourceCompatibility = 1.8
 	targetCompatibility = 1.8
+	options.compilerArgs += "-Werror"
 }
 
 // This module also builds Kotlin code and the compileKotlin task naturally depends on