random jdk9-dev build error

[Jim Laskey (Oracle)]

After a clean got

dtrace: failed to compile script 
/Projects/jdk9-dev/build/macosx-x86_64-normal-server-fastdebug/hotspot/variant-server/support/dtrace/hotspot_jni.h.d:
 line 1: empty D program translation unit

second time worked fine.