...had been missing.  Old dmake-based build system did not add -source/-target
when using gcj (unless gcj really was Eclipse Java Compiler, in which case those
-source/-target values were tunneled in via JAVAFLAGS)---hopefully all this is
no longer necessary.

(Also removed a single use of JAVA_TARGET_FLAG that was nowhere defined.)

Change-Id: Ic3596691b622be45e151333981f8f236d11825b4