ICU-22714 fix zos build, use OpenXL

[alexgubanow]

I have fixed the git clone of this repo on zos and moved build from old XLc compiler to new OpenXL compiler. More details https://unicode-org.atlassian.net/browse/ICU-22714 As of now:

• tests are passing, some issues with files not being UTF-8 on zos, will address that in separate PR
• results of build was tested internally, we have own test suite
• following files had no BOM, need to fix tool that is used to generate those: icu4c/source/data/misc/currencyNumericCodes.txt icu4c/source/data/misc/icustd.txt icu4c/source/data/misc/zoneinfo64.txt

Checklist

• [x] Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22714
• [x] Required: The PR title must be prefixed with a JIRA Issue number.
• [x] Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• [x] Required: Each commit message must be prefixed with a JIRA Issue number.
• [ ] Issue accepted (done by Technical Committee after discussion)
• [x] Tests included, if applicable
• [x] API docs and/or User Guide docs changed or added, if applicable