[9] RFR 8172990: [AOT] Missing GC scan of _metaspace_got array containing Klass*

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/8172990/webrev
https://bugs.openjdk.java.net/browse/JDK-8172990

The code which scans _metaspace_got array is commented out. 
Unfortunately called AOTCompiledMethod::metadata_do() does not iterate 
over all Klass* which could be referenced by AOT code by accessing 
_metaspace_got array.

Added _metaspace_got array scan back but removed duplicated code from it.
Changed _metaspace_got array generation during AOT compilation to avoid 
having non Klass* or NULL values in it.
Added missing Method* scan in non virtual call stubs.
Cleaned up unused code and old invalid comments.

Thanks,
Vladimir