Open XL Toolchain Changes

[Deigue]

Contains all the initial required toolchain changes to start using Open XL compiler with z/OS builds.

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Keeping as draft state until I have verified it does not interfere with z/OS XLC Builds.

[Deigue]

@joransiu @keithc-ca Created draft PR for toolchain changes for some early feedback. Let me know if I should add/tag anyone who might recommend good practice changes that might be needed/missing from these.

[Deigue]

I will undo the UMA/mk updates (they were some ported commits of some much earlier attempts at open xl compilation) and verify that it doesn't impact the current compilation with java 21, along with the above suggestions. Thanks for the feedback.

[pshipton]

We'll also have to verify IBM Java 8 compilation isn't impacted.

[Deigue]

Removed all changes that aren't related to use of cmake and addressed the comments above or added comments as necessary. I have also verified now that this maintains the compilation progress so-far for Open XL.

Pending verification of a standard xlc build and a java 8 build to ensure no impact.

[Deigue]

Removed compiler.mk and indented the changes in runtime/cmake/platform/os/zos.cmake appropriately.

j21 passed

[Deigue]

Comments above addressed ... Launched builds j21: passed and java 8: success, unrelated 3 errors to verify https://github.com/eclipse-openj9/openj9/commit/3d59835a9ce3a54cb3e6cfb0a17dfb05cef4803f

Once those check out, will bring PR out of draft.

[Deigue]

Thanks, I've addressed the above comments.

[Deigue]

@keithc-ca This one is ready for a re-check.

[Deigue]

Rebased with master, confirmed passing with java 8 and java 21 builds.

[keithc-ca]

Jenkins compile aix jdk21