Add ARM kCpuArchitecture string for Linux platforms

[davidalo]

Description

ARM architecture is working as expected for me using Auth and Database services, the unique problem I had was the kCpuArchitecture string declaration

[Add kCpuArchitecture]: # Add ARM kCpuArchitecture string for Linux platforms

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Testing

Manually tested using examples.

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Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

For more information, open the CLA check for this pull request.

[davidalo]

I signed CLA, it should be ready.

[jonsimantov]

Approved, with the caveat that we have not tested (and do not support) using the SDK on ARM Linux at this time.

It also appears to still see your CLA as unsigned, could you visit the URL linked above and double-check everything is in order?

Thanks!