RFR: 8252233: Enable debug-image target to support producing a pure debug image package

[Andrew Leonard]

Hi,
Please may I request a sponsor and review for this build enhancement to 
provide a pure debug "image", for those developers that want to accompany 
a straight jdk image with a debug-image when needed:
    https://bugs.openjdk.java.net/browse/JDK-8252233
    webrev: http://cr.openjdk.java.net/~aleonard/8252233/webrev.00/
We have been providing this as part of the openj9 builds at AdoptOpenJDK 
for a while now, and would like to contribute it upstream to openjdk.

Thanks
Andrew

Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
internet email: andrew_m_leonard at uk.ibm.com 

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