RFR: JDK-8037238: JDK 9 images don't rebuild when access bridge jars rebuild

[Erik Joelsson]

When rebuilding after touching a java source file in AccessBridge, the 
classes were recompiled but the jars were not rebuilt. This was caused 
by a bug in the macro CacheFind. The cache in this case contained the 
directory $(JDK_OUTPUTDIR)/classes. The jar was built from the src dir 
$(JDK_OUTPUTDIR)/classes_ab. The matching code found the latter to be a 
subdir of the former and so chose to use the cache and of course found 
nothing. I fixed the test to either match with a trailing slash or make 
an exact match.

I also added a warning in SetupArchive so that we will catch empty 
dependency lists faster next time.

Bug: https://bugs.openjdk.java.net/browse/JDK-8037238
Webrev: http://cr.openjdk.java.net/~erikj/8037238/webrev.root.01/

/Erik