[13u] RFR: 8238676: jni crashes on accessing it from process exit hook

[Ekaterina Vergizova]

Hello,
I would like to backport the fix for 8238676 and its regression fix 8240603 to 13u. 
They are already included into 11u.

JBS: https://bugs.openjdk.java.net/browse/JDK-8238676
Original patch: https://hg.openjdk.java.net/jdk/jdk/rev/80e4a066342d
Webrev for 13u: http://cr.openjdk.java.net/~yan/8238676/webrev.00/

The patch for 8238676 applies almost cleanly except for: 
- changes for make/test/JtregNativeHotspot.gmk apply manually due to different context (8179317 is not in 13u)
- the second hunk of src/hotspot/share/prims/jni.cpp applies manually due to different context (8234739 is not in 13u) 

The patch for 8240603 applies cleanly.

Tested with tier1 on Windows, the test added in 8238676 failed before the fixes and passes after.

Thanks,
Ekaterina