8212958: Allow Klass::_subklass and _next_sibling to have unloaded classes
Summary: Don't return unloaded klasses. Make sure access is protected by Compile_lock.
Reviewed-by: eosterlund, dlong
/build/
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nbproject/private/
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test/nashorn/script/external
test/nashorn/lib
NashornProfile.txt
**/JTreport/**
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