Run javac with encoding=utf8

The behaviour of javac changed such that comments containing utf-8
characters is now an error unless you specify the encoding of the file.

Belonging to [master]:
  - #2366

Author: sjoelund

SimulationRuntime/java_interface/Makefile.in

@@ -6,7 +6,7 @@ include Makefile.common
 modelica_java.jar: $(java_sources)
 	@echo "* Compiling modelica_java.jar"
 	@rm -rf bin-jar; mkdir bin-jar
-	@"$(JAVAC)" -source 6 -cp "$(antlr)" -d bin-jar $(java_sources)
+	@"$(JAVAC)" -encoding utf8 -source 6 -cp "$(antlr)" -d bin-jar $(java_sources)
 	@$(JAR) cf modelica_java.jar $(java_sources:src/%=-C src %) $(resources:src/%=-C src %) -C bin-jar . || (rm $@ && false)
 test: $(java_sources)
 	rm -rf bin-test; mkdir bin-test