Fix build of Monocle for Linux

DESCRIPTION

JavaFX with Monocle fails to compile when building for embedded systems like the Raspberry Pi.

SYSTEM / OS / JAVA RUNTIME INFORMATION

The system is Ubuntu 20.04.1 LTS with OpenJDK 14.0.2, Ant 1.10.7, and Gradle 6.3. The build environment is set up by sourcing the following shell script:

    # Sets up the environment for building JavaFX
    syspath=/usr/sbin:/usr/bin:/sbin:/bin

    export JAVA_HOME=/usr/lib/jvm/java-14-openjdk-amd64
    export ANT_HOME=/usr/share/ant
    export GRADLE_HOME=$HOME/opt/gradle-6.3

    # JDK_HOME and PATH are required by the build
    export JDK_HOME=$JAVA_HOME
    export PATH=$GRADLE_HOME/bin:$ANT_HOME/bin:$JAVA_HOME/bin:$syspath

STEPS TO REPRODUCE

Follow the instructions for building JavaFX with Monocle on the following two pages:

Building OpenJFX
https://wiki.openjdk.java.net/display/OpenJFX/Building+OpenJFX

Cross Building for ARM Hard Float
https://wiki.openjdk.java.net/display/OpenJFX/Cross+Building+for+ARM+Hard+Float

Build the latest JavaFX 16 with the command:

    $ gradle -PCOMPILE_TARGETS=armv6hf

EXPECTED RESULTS

The build should end with the message "BUILD SUCCESSFUL."

ACTUAL RESULT

The build ends with the message "BUILD FAILED" due to the following error:

  /home/ubuntu/src/jfx/modules/javafx.graphics/
    src/main/native-prism-es2/monocle/MonocleGLFactory.c:116:19:
  error: ‘RTLD_DEFAULT’ undeclared (first use in this function)

SOURCE CODE FOR AN EXECUTABLE TEST CASE

None

WORKAROUND

None