tools: Warn when ARMC5 is no longer supported

[Patater]

Summary of changes

For backwards compatibility reasons, as the Mbed tools must be able to build any online-compiler-supported version of Mbed, revert back to emitting a warning when ARMC5 is used. This will enable ARMC5 to continue working in the online compiler for Mbed OS 5 and other previous versions. ARMC5 remains unsupported in Mbed 6.

Impact of changes

None

Migration actions required

None

Documentation

No additional documentation required.

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[ciarmcom]

@Patater, thank you for your changes.
@ARMmbed/mbed-os-tools @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

If this goes to master, and we apply this to the online compiler - will it work for 5.15.x as well ? we dont need to propagate this patch to 5.15 branch as well?

Otherwise, this make sense

[mark-edgeworth]

This looks ok as a first step, although all this does is to change the error to a warning of course. The proof here will be whether the code actually still generates a working build for ARMC5...

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 6 of 6 test jobs passed
Build number : 1
Build artifacts

[andypowers]

Approved.

[Patater]

If this goes to master, and we apply this to the online compiler - will it work for 5.15.x as well ? we dont need to propagate this patch to 5.15 branch as well?

No, this won't be needed on the 5.15 branch. The online compiler uses the tools from the latest version of Mbed.

Sorry this doesn't make sense.