Some applications, like the Jetbrains IDEs, check for a suffix to
determine if a stable JDK is used.
This flag was already passed for older versions, but it got lost for
OpenJDK 14+.
* update two explicit references to jdk14 to just jdk, which no longer
points at jdk8 after #89731.
* patch an explicit -XX:+UseConcMarkSweepGC to -XX:UseG1GC, as the
former now throws an error (after having been deprecated since jdk 9)
