AArch64: Create configuration for native build

[knn-k]

Build of AArch64 Linux runtime requires cross-compilation environment in Docker on x86-64 Linux.
There is a request for building the runtime natively on AArch64 Linux.

[jdekonin]

Trying looking at what @dsouzai and @JamesKingdon have done via #1159 and #712

[knn-k]

The file runtime/jilgen/module.xml uses qemu-aarch64 for running constgen in the cross build. I have found I can build the runtime natively on AArch64 Linux by changing that file.
Now my question is: How can you detect the native/cross-building environment in module.xml? Is there any flag that can be used for that purpose?

The AArch64 build does not support DDR at the moment (#5221). When we support it, runtime/ddr/module.xml also needs to be modified because it uses qemu-aarch64.

[hangshao0]

It seems that we do not have an existing flag for this purpose. You might need to add a new flag. Not sure if it is worth the effort, as uma is going to be replaced by cmake shortly. Adding a new spec might be an easier solution for now.

[knn-k]

@hangshao0 Thank you for your suggestion. What is the plan for moving to cmake?

[hangshao0]

What is the plan for moving to cmake?

@dnakamura

[pshipton]

Note there is a cmake plan of sorts in #90

[knn-k]

I opened #5321 and ibmruntimes/openj9-openjdk-jdk11#149 adding a new flag to j9.flags as a short-term solution.