Add an exception for ARMC5 toolchain build

[rajkan01]

Summary of changes

The Arm Compiler 5 is no longer supported so removed the deprecate warning and added the exception in the build tool to stop building with ARM compiler 5.

Impact of changes

With these changes, Arm compiler 5 build fails

Migration actions required

Upgrade the enviroment to use Arm Compiler 6 refer

Documentation

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[x] 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

@evedon @madchutney

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[ciarmcom]

@rajkan01, thank you for your changes.
@madchutney @evedon @ARMmbed/mbed-os-tools @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

Is this warning-error all we need do - there is still code related to ARM5 in the tools/targets, we remove it separately but still within 6.0 version?

[mark-edgeworth]

There are currently 68 references to ARMC5 in mbed-os. What is the plan to remove these?

[0xc0170]

Started CI while we complete the review

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts

[0xc0170]

Not yet ready for integration, @bulislaw Please approve

[bulislaw]

This is a good first step, but I'd like us to remove all the dead code that's there for ARMC5 support and compatibility.