UMA build is not supported on AArch64 macOS

[knn-k]

Build fails with the following message when --with-cmake=no is specified on AArch64 macOS. The spec file for AArch64 macOS is missing in the buildspecs directory.

Universal Makefile Adapter - for J9, version 2.5.1

Could not find osx_aarch64.spec file.

[knn-k]

I enabled only CMake build in my PR #13700.

[keithc-ca]

In answer to the question ibmruntimes/openj9-openjdk-jdk11#780 (comment), I don't know of any documentation that would help.

I would start with a copy of buildspecs/osx_x86-64.spec replacing x86 references with suitable replacements for aarch64. I expect changes will be required to makefiles like runtime/makelib/targets.mk.osx.inc.ftl.

[knn-k]

Thank you for the comment.

I don't have the environment to try on, but I think the UMA build for x86-64 macOS does not work now.

[knn-k]

I found a problem while trying UMA build, and opened PR #19521 as the fix. CMake build does not fail with the problem.

[knn-k]

It turned out it requires much more work to enable UMA build than I had thought.
I don't think it is worth spending time, and I opened PR #19538 instead.