https://bugs.openjdk.java.net/browse/JDK-8139935
The reason this “works” for a non-bootcycle build is because a JDK 9 javac
won't enforce the “hidden packages” rules when running on a non-JDK 9 platform.
diff -r a8a8604f890f make/gensrc/Gensrc-jdk.vm.ci.gmk
--- a/make/gensrc/Gensrc-jdk.vm.ci.gmk Sat Oct 17 19:40:30 2015 -0400
+++ b/make/gensrc/Gensrc-jdk.vm.ci.gmk Tue Oct 20 09:57:02 2015 -1000
@@ -77,6 +77,7 @@ PROCESSOR_PATH := $(call PathList, \
$(MKDIR) -p $(@D)
$(eval $(call ListPathsSafely,PROC_SRCS,$(@D)/_gensrc_proc_files))
$(JAVA_SMALL) $(NEW_JAVAC) \
+ -XDignore.symbol.file \
-sourcepath $(SOURCEPATH) \
-implicit:none \
-proc:only \
