Is there a way to set "Created-By" in MANIFEST.MF to the forked Java version


I am running builds on Gradle 3.3 running in Java 1.7
The compilations themselves are done in a different version of Java (1.6) using the following:

tasks.withType(JavaCompile) {
    options.fork = true
    options.forkOptions.executable = "C:/WebSphere8/AppServer/java/bin/javac.exe"
    sourceCompatibility = JavaVersion.VERSION_1_6
    targetCompatibility = JavaVersion.VERSION_1_6

My problem is that in my JAR task, I want to specify the version of Java being used to compile the JAR, not the version of Java that Gradle is using to run atop.

If I attempt to use the following in my manifest, it pulls in the Java 1.7 version

manifest {
    attributes (
        'Created-By': System.getProperty('java.version') + ' (' + System.getProperty('java.vendor') + ')'

Does anyone know a way of obtaining the forked Java version?
Note: The above samples are overly simplified. I know I set the fork up in the first place, so I could hard code the Created-By value, but that’s not what I need. I just need to report the forked compiler version in the Manifest.