RFR (S) 8173361: various crashes in JvmtiExport::post_compiled_method_load

[coleen.phillimore at oracle.com]

Summary: Don't post information which uses metadata from unloaded nmethods

Tested tier1-3 and 100 times with test that failed (reproduced failure 
without the fix).

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8173361.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8173361

Thanks,
Coleen