Run ErrorProne in OpenJDK9

Use the OpenJDK9 javac to run ErrorProne by adding it to
-processorpath and using -Xplugin:ErrorProne.

Bug: 69485063
Test: m RUN_ERROR_PRONE=true javac-check
Change-Id: I0496006b71b70766ef16d57753cbcf037897799c
diff --git a/java/config/makevars.go b/java/config/makevars.go
index 0e62274..8dfd398 100644
--- a/java/config/makevars.go
+++ b/java/config/makevars.go
@@ -52,14 +52,15 @@
 
 	ctx.Strict("TURBINE", "${TurbineJar}")
 
-	if ctx.Config().IsEnvTrue("RUN_ERROR_PRONE") {
-		ctx.Strict("TARGET_JAVAC", "${ErrorProneCmd}")
-		ctx.Strict("HOST_JAVAC", "${ErrorProneCmd}")
-	} else {
-		ctx.Strict("TARGET_JAVAC", "${JavacCmd} ${CommonJdkFlags}")
-		ctx.Strict("HOST_JAVAC", "${JavacCmd} ${CommonJdkFlags}")
+	if ctx.Config().RunErrorProne() {
+		ctx.Strict("ERROR_PRONE_JARS", strings.Join(ErrorProneClasspath, " "))
+		ctx.Strict("ERROR_PRONE_FLAGS", "${ErrorProneFlags}")
+		ctx.Strict("ERROR_PRONE_CHECKS", "${ErrorProneChecks}")
 	}
 
+	ctx.Strict("TARGET_JAVAC", "${JavacCmd} ${CommonJdkFlags}")
+	ctx.Strict("HOST_JAVAC", "${JavacCmd} ${CommonJdkFlags}")
+
 	if ctx.Config().UseOpenJDK9() {
 		ctx.Strict("JLINK", "${JlinkCmd}")
 		ctx.Strict("JMOD", "${JmodCmd}")