[MCOMPILER-457] Warn about warn-config conflicting values

Author: pzygielo

src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java

@@ -732,6 +732,12 @@ public void execute()
 
  compilerConfiguration.setFailOnWarning( failOnWarning );
 
+ if ( failOnWarning && !showWarnings )
+ {
+ getLog().warn( "The property failOnWarning is set to true, but showWarnings is set to false." );
+ getLog().warn( "With compiler's warnings silenced the failOnWarning has no effect." );
+ }
+
  compilerConfiguration.setShowDeprecation( showDeprecation );
 
  compilerConfiguration.setSourceVersion( getSource() );