Specifying Java version when using ant-build-system

[Danny Milosavljevic]

Hi,

how can I specify that I need a Java 1.8 compiler and source level when using 
ant-build-system?

Also, guix/build-system/ant.scm says:

(define* (ant-build store name inputs
                    #:key
                    (tests? #t)
                    (test-target "tests")
                    (configure-flags ''())
                    (make-flags ''())
                    (build-target "jar")
                    (jar-name #f)
                    (phases '(@ (guix build ant-build-system)
                                %standard-phases))
                    (outputs '("out"))
                    (search-paths '())
                    (system (%current-system))
                    (guile #f)p
                              ^^^ what does this mean?
                    (imported-modules %ant-build-system-modules)
                    (modules '((guix build ant-build-system)
                               (guix build utils))))