https://github.com/bytedeco/javacpp/wiki/Gradle
https://gist.github.com/bongole/05021bdd1f21578e1f6f

Usage: java -jar javacpp.jar [options] [class or package (suffixed with .* or .**)]
where options include:
    -classpath <path>      Load user classes from path
    -encoding <name>       Character encoding used for input and output files
    -d <directory>         Output all generated files to directory
    -o <name>              Output everything in a file named after given name
    -nocompile             Do not compile or delete the generated source files
    -nodelete              Do not delete generated C++ JNI files after compilation
    -header                Generate header file with declarations of callbacks functions
    -copylibs              Copy to output directory dependent libraries (link and preload)
    -copyresources         Copy to output directory resources listed in properties
    -jarprefix <prefix>    Also create a JAR file named "<prefix>-<platform>.jar" !!! otherwise - do not create a jar
    -properties <resource> Load all properties from resource
    -propertyfile <file>   Load all properties from file
    -D<property>=<value>   Set property to value
    -Xcompiler <option>    Pass option directly to compiler

at manifest
Main-Class: org.bytedeco.javacpp.tools.Builder
http://bytedeco.org/javacpp/apidocs/org/bytedeco/javacpp/tools/Builder.html
https://github.com/bytedeco/javacpp/blob/master/src/main/java/org/bytedeco/javacpp/tools/Builder.java
https://github.com/bytedeco/javacpp/blob/master/src/main/java/org/bytedeco/javacpp/tools/Generator.java

javaexec {
    main = 'org.bytedeco.javacpp.tools.Builder'
    classpath = files(configurations.javacpp.asPath)
    args = [
        '-cp', "$classesDir",
        '-properties', 'android-x86',
        '-Dplatform.root=/usr/local/opt/android-ndk',
        '-Dplatform.compiler=/usr/local/opt/android-ndk/toolchains/x86-4.6/prebuilt/darwin-x86_64/bin/i686-linux-android-g++',
        "-Dplatform.includepath=sources/cxx-stl/gnu-libstdc++/4.6/include/:sources/cxx-stl/gnu-libstdc++/4.6/libs/x86/include/:$projectDir/jni/include",
        "-d", "$jniDir/x86/"
    ]
}

Builder {
...
    int compile(
        String[] sourceFilenames,
        String outputFilename,
        ClassProperties properties,
        File workingDirectory) throws IOException, InterruptedException {
        ...
        logger.info(text);

        ProcessBuilder pb = new ProcessBuilder(command);
        // Use the library output path as the working directory so that all
        // build files, including intermediate ones from MSVC, are dumped there
        pb.directory(workingDirectory);
        if (environmentVariables != null) {
            pb.environment().putAll(environmentVariables);
        }
        return pb.inheritIO().start().waitFor();
    }