RFR: JDK-8188050: UnsatisfiedLinkError after repo consolidation

[Erik Joelsson]

After the repo consolidation, I missed updating the 
IncludeCustomExtension calls for the JtregNative*.gmk files. This causes 
tests to fail for us since the native libraries have not been built.

Bug: https://bugs.openjdk.java.net/browse/JDK-8188050
Webrev: http://cr.openjdk.java.net/~erikj/8188050/webrev.01/

/Erik