tweak JVM options to better handle project cardinality

[bjaglin]

Lately, we have seen many warnings like this on JDK8.

[warn] In the last 10 seconds, 8.954 (97.6%) were spent in GC. [Heap: 0.20GB free of 1.76GB, max 1.78GB] Consider increasing the JVM heap using `-Xmx` or try a different collector, e.g. `-XX:+UseG1GC`, for better performance.

The cardinality/complexity of the build has greatly increased with #2034 and #2023, so it's probably time for a little refresh of the JVM options.