Force on the CXX11_ABI flag

[a-maurice]

Description

Provide details of the change, and generalize the change in the PR title above.

The Linux Unity editor was crashing in the Firestore testapp. From what I can tell, the Unity editor was likely build with this option enabled, and mixing the library without it was the cause of the crash. So we will force the option to always be on for Linux builds. Note that standalone builds were not crashing, so it was likely just a problem with the Unity editor being built with that option.

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Testing

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Type of Change

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• 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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[a-maurice]

Desktop build: https://github.com/firebase/firebase-unity-sdk/actions/runs/2242859483

[dconeybe]

Details about the _GLIBCXX_USE_CXX11_ABI preprocessor define are here: https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html

[github-actions]

❌  Integration test FAILED

Requested by @a-maurice on commit 91f0096
Last updated: Fri Apr 29 13:28 PDT 2022
View integration test log & download artifacts

Failures	Configs
analytics	[TEST] [FLAKINESS] [2019] [macos] [1/5 Platform(s): iOS] [1/2 Test Device(s): ios_target]
firestore	[TEST] [FAILURE] [2019] [macos] [1/5 Platform(s): Android] [1/2 Test Device(s): android_target]
messaging	[TEST] [ERROR] [2019] [macos] [2/5 Platform(s): Android iOS] [All 2 Test Device(s)]
storage	[BUILD] [ERROR] [2019] [macos] [All 3 Platform(s)]