RFR (T) 8248271: linux-x86-zero build failure

[coleen.phillimore at oracle.com]

See bug for description.  A declaration was missing in os_linux_zero.hpp

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8248271.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8248271

mach5 remote-build -b 
linux-x64-zero,linux-x64-zero-debug,linux-x86-zero,linux-x86-zero-debug

Thanks,
Coleen

ps. I didn't break this!