mbed-trace: Remove ARM Compiler 5 support

[hugueskamba]

Summary of changes

ARM Compiler 5 is no longer actively supported and was superseded in
Mbed OS by ARM Compiler 6.

Impact of changes

Breaking change: The binary generated from ARM Compiler 5 cannot be relied on as support has been dropped.

Migration actions required

Use Arm Compiler 6.

Documentation

N/A

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[X] 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

@SeppoTakalo @evedon

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[ciarmcom]

@hugueskamba, thank you for your changes.
@SeppoTakalo @evedon @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

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

[SeppoTakalo]

I don't understand the benefit of doing this?

This library might be used on other projects using Arm C 5.

Dropping support from Arm Compiler 5 should not mean that we start actively preventing compilation on it.

[evedon]

I don't understand the benefit of doing this?

This library might be used on other projects using Arm C 5.

Dropping support from Arm Compiler 5 should not mean that we start actively preventing compilation on it.

The requirement is to remove any ARMC5 compiler specific code to cleanup the code base.
The benefit is a smaller / cleaner code base.
If we consider that some libraries might be used on other projects and that they should be excluded from this requirement then let's review internally.
@bulislaw

[bulislaw]

Hi @SeppoTakalo, We are removing ARMC5 support from the OS to simplify the sources, remove dead code and not carry dead weight with us as the compiler is deprecated by DSG. I agree that in this case it doesn't have a big impact on anything. But realistically speaking do you expect anyone removing the sources of mbed-trace from Mbed OS and using it elsewhere? If you think it makes actual sense to keep it for mbed-trace I don't mind omitting this.

[SeppoTakalo]

https://github.com/ARMmbed/mbed-trace/
As its origin, is an external library.
And yes, it is used outside Mbed OS even currently.

I know why ARMC5 code is dropped, and I agree that the dead code should be removed.
But I still propose that some pieces of the code, that exists outside of OS, or where the change could have negative impact, we leave as is.

This trace library is used by Pelion Client on all platforms. I therefore propose that we don't touch it now.

[evedon]

I agree that there is no big impact in keeping ARMC5 references in mbed-trace but we should aim to remove dead code in other libraries. So let's close this PR.