RFR(XS): 8073754: Zero/PPC: StackOverflowError during build in javadoc processing.

[Severin Gehwolf]

Hi,

Could somebody please review and sponsor this Zero-only change?

It fixes a build problem of OpenJDK 9 Zero on PPC64. That architecture
seems to be notoriously stack hungry and needs an increased minimal
stack in order to build and self-build JDK 9.

Bug: https://bugs.openjdk.java.net/browse/JDK-8073754
Webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8073754/webrev.02/

Thanks,
Severin