lang/abcl: use java portgroup to set jdk compiler

ABCL builds under openjdk6,openjdk7,openjdk8,openjdk11.  For openjdk13
and beyond we will need to bump the compilation target.  Variants to
do that forthcoming.

lang/abcl/Portfile

@@ -6,6 +6,7 @@ name			    abcl
 version			    1.6.0
 revision            0
 categories		    lang java
+PortGroup           java 1.0
 license             GPL-2
 maintainers		    {easieste @easye} openmaintainer
 description		    A Common Lisp implementation that runs on the JVM
@@ -31,8 +32,11 @@ checksums           md5     d4fc29f4f600db0e77e32b49f91d518c \
                     sha256  893fce815d3fc9a3aa250c78ff84ed2e51b702f71cb11e1befc2a2ec9c666b43 \
                     size    2509074
 
+
 depends_build       port:apache-ant
 
+java.version        11
+java.fallback       openjdk11
 use_configure       no
 
 build.cmd           ant