Create a new aggregate tool from existing tools.
Constructs a new set of java toolchain for incremental compilation.
The scalaInstance being used in this incremental compile. Used if we need to append scala to the classpath (yeah.... the classpath doesn't already have it).
Classpath options configured for this incremental compiler. Basically, should we append scala or not.
If this is defined, the location where we should look for javac when we run.
A new set of the Java toolchain that also includes and instance of xsbti.compile.JavaCompiler