RFR(XS): 8211210: [lworld] Compilation fails with "default value may not be null" with -XX:+StressReflectiveCode

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8211210/webrev.00/

With +StressReflectiveCode, layout is not a constant even for allocation
of known types which causes the RawDefaultValue to be set when it's not
expected. The check for layout_con here is I think too conservative so
simply removing it and relying on type checks should be good enough.

Roland.