RFR: 8223186: HotSpot compile warnings from GCC 9

[Yasumasa Suenaga]

Hi all,

Please review this change:

   JBS: https://bugs.openjdk.java.net/browse/JDK-8223186
   webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8223186/webrev.00/


I saw following warnings when I compiled HotSpot with GCC 9 on Fedora 30 
due to -Wwrite-strings, -Wstringop-truncation and -Wclass-memaccess.
I filed all warnings to JBS.


Thanks,

Yasumasa