RFR: 8014514: Fix jvm args for sjavac

[Erik Joelsson]

This patch tries to be smarter when figuring out optimal jvm args for 
sjavac, especially if the jvm used is 32bit.

http://cr.openjdk.java.net/~erikj/8014514/webrev.root.01/
For this to work properly, two patches to the sjavac src langtools are 
also needed, but they will be handled in separate bugs and code reviews.

/Erik