RFR(XS): 8211837: Creation of the default CDS Archive should depend on ENABLE_CDS

[Volker Simonis]

Hi,

can I please have a review for the following trivial build fix:

http://cr.openjdk.java.net/~simonis/webrevs/2018/8211837/
https://bugs.openjdk.java.net/browse/JDK-8211837

It makes no sense to try to create a default CDS archive on VMs which
don't support CDS at all. We already have '--enable_cds' which
defaults to 'true' on all platforms except AIX.

The check for '--enable_cds_archive' should use the result of
'--enable_cds' (which is saved in "ENABLE_CDS") and only enable
default archive creation if CDS is enabled.

Failure to do so currently breaks the AIX build (after JDK-)8202951 was pushed).

Thank you and best regards,
Volker