back-port Use the actual system-packages from the JVM for export

[gireeshpunathil]

Fixes #194 for PDE-build

Refs: #624

Refs: eclipse-pde/eclipse.pde.build#16

(commit of this PR should be paired together with the commit in the referenced PR in eclipse.pde.build repo, as they constitute a single commit logically, but got split up physically due to the the fact that they were in two repos then)

[gireeshpunathil]

@HannesWell - I split the commit into two and backported one part here, and the other in the pde build repo. I am struggling to build the combination locally (even after cloning both the repos in the same project, I get a lot of errors, trying to get some meaning of it), but the backport should work in theory, as the merge was clean.

Please have a look!

[HannesWell]

@HannesWell - I split the commit into two and backported one part here, and the other in the pde build repo. I am struggling to build the combination locally (even after cloning both the repos in the same project, I get a lot of errors, trying to get some meaning of it), but the backport should work in theory, as the merge was clean.

I have to admit that I don't fully recall how pde.ui (which used to be the name for this repo) and pde.build are build together, but I believe that pde.build used to be independent and pde.ui depended on pde.build, so you should be able to build the latter standalone. A quick look at https://github.com/eclipse-pde/eclipse.pde.build/blob/R4_23_maintenance/org.eclipse.pde.build/pom.xml shows that on the maintenance branch the parent has a SNAPSHOT-version (which is likely not available anymore after the release) and also has a unexpected group- and artifactId.
I recommend you look up how you build the maintenance branches at your build system and replicate the maven commands locally or work it out with @vik-chand. :)

That being said and looking at this change, I remember that the change now in this PR is only a small (probably not noticeable) performance optimization but not a functional change. You can see that by looking in the implementation of the old code.
Therefore I think it is not necessary to back-port it.

[gireeshpunathil]

@HannesWell - thanks for all the tips, I am now able to validate the back-port: by building both on the command line, and through eclipse.

• building in the command line was very tricky: it involved replacing the occurrences of 4.23.0-SNAPSHOT to 4.29.0-SNAPSHOT in all the pom.xml files
• building in eclipse was easy: source both the reps, import o.e.pde.core and o.e.pde.build, downgrading the org.eclipse.jdt.launching bundle version to match what was available in 4.23 timeframe.
• I am also able to validate that the reported issue is fixed without the change in this PR.

so going to close this PR in lieu of eclipse-pde/eclipse.pde.build#16. let me know if we are on the same page; and also pls review that PR.

thanks once again! lots of learning indeed!

[HannesWell]

You're welcome and I'm glad you were successful finding the tricky bits. 👍