RFR(S) 8226406: JVM fails to detect mismatched or corrupt CDS archive

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8226406

webrev: http://cr.openjdk.java.net/~ccheung/8226406/webrev.00/

This bug was found during a bootcycle build when a shared archive built 
by a 64-bit JDK version is used by a 32-bit JDK version. It is due to 
some of the important header fields such as the _jvm_ident was not 
checked prior to accessinng other fields such as the _paths_misc_info_size.

This fix involves checking most the fields in CDSFileMapHeaderBase 
before accessing other fields.

Testing: tiers 1-3.

thanks,

Calvin