RFR (XS): 8005592: ClassLoaderDataGraph::_unloading incorrectly defined as nonstatic in vmStructs

[Mikael Vidstedt]

Please review the following change.

Background:

The _unloading field is a static field in ClassLoaderDataGraph (in 
classLoaderData.hpp) and should therefore be defined using static_field, 
as opposed to nonstatic_field, in vmStructs.

Apart from changing from nonstatic_field to static_field I also added an 
assert in the CHECK_NONSTATIC_VM_STRUCT_ENTRY macro to make sure any 
field offsets are within the bounds of the corresponding structs. The 
assert triggers for _unloading before the change to static_field.

The change passes JPRT.

http://cr.openjdk.java.net/~mikael/8005592/webrev.00/

Thanks,
Mikael