travis: Reject changes to tools

[Patater]

Summary of changes

As part of freezing the current Mbed tools, reject any changes to tools that would require a re-release of the tools for the online compiler. This enables us to focus our effort on developing a far more maintainable set of tools, rather than on performing existing tool releases which are very error prone, time consuming, and labor intensive.

No new releases of the online tools are planned. To keep feature parity between the offline and online tools (i.e. to keep the online compiler working), we are locking the Mbed OS tools.

Impact of changes

None

Migration actions required

None

Documentation

None

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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)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

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Reviewers

@jamesbeyond @rwalton-arm

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[ciarmcom]

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

[Patater]

• Failing test run with a "bad commit": https://travis-ci.org/github/ARMmbed/mbed-os/jobs/712523967
• Passing test run with no "bad commit": https://travis-ci.org/github/ARMmbed/mbed-os/jobs/712525828

Pull request has been modified.

[Patater]

Add a bad commit to test Travis CI error message.

[Patater]

Bad Travis CI run for test purposes: https://travis-ci.org/ARMmbed/mbed-os/jobs/714917860

Failure: Frozen files were modified
tools/toolchains/gcc.py
Please see https://os.mbed.com/blog/entry/Introducing-the-new-Mbed-Tools/ 
for why we've frozen the legacy tools.

[Patater]

Removed bad commit.

[adbridge]

CI started