Move the custom javac option to the Java subsystem.

Review Request #4141 — Created Aug. 6, 2016 and submitted

stuhood, zundel
It was initially an option on ZincCompile.  But putting it on Java
allows us to have plugins depend on the custom javac instead of
always depending on the JDK's tools.jar.  This solves mismatch
issues where we depend on the regular tools.jar when compiling
a plugin, but then that plugin runs against the custom javac.

CI passes:

  1. Ship It!
    1. Thanks Eric. Weirdly, I didn't get an email notification of your review, and not for the first time. I'm wondering if that's my settings or yours?

    2. Looks like when rbcommons posts my replies to the pants-reviews list they keep getting caught up as spam and I have to 'approve' them on the pants-reviews googlegroups website. I just went through the pants-reviews list and made sure I was still configured to receive mail and I am. Not sure what's going on.

Review request changed

Status: Closed (submitted)

Change Summary: