[13u] RFR: 8224851: AArch64: fix warnings and errors with Clang and GCC 8.3

[Sergey Nazarkin]

Original change:
http://hg.openjdk.java.net/jdk/jdk/rev/e53ec3b362f4
https://bugs.openjdk.java.net/browse/JDK-8224851

Review for 11u:
https://mail.openjdk.java.net/pipermail/jdk-updates-dev/2020-January/002432.html


I personally have not found any build issue with GCC8.4 (cross tool from ubuntu 18.04). However the patch touches too many files that may introduce backport problem in the future. 

It is not applied cleanly due to modifications caused by aarch64 simulator removal. Luckily only os_linux_aarch64.cpp is affected

Webrev
http://cr.openjdk.java.net/~snazarki/webrev/8224851/



Sergey Nazarkin