Note: this change does not make build sequential. Build system still
uses it's way to parallelize the build.
The only effect of this change is not to pass unsupported -j option
to Makefile when nixpkgs default will be switched to
enableParallelBuilding = true;
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)
