Fix toolchain selection and packages on linux x86

[jonsimantov]

Description

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

There were several issues preventing Linux x86 from being built correctly since the removal of vcpkg.

First, we were no longer setting the linux_32.cmake toolchain file in build_desktop.py - this has been fixed.

Second, 32-bit builds could not locate 32-bit versions of certain libraries. This has been fixed by adding the 32-bit package directory to the PKG_CONFIG_PATH environment variable in both source and packaged builds.

Finally, libsecret 32-bit was not being installed correctly due to package conflicts, which aptitude decided to resolve by simply not installing libsecret. Instead, on github runners, remove the conflicting packages as part of the same aptitude command line that does the installation, so it uses that as its method of resolution and does install libsecret.

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Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Running expanded matrix integration tests against packaged and source builds.

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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.

[github-actions]

❌  Integration test FAILED

Requested by @jonsimantov on commit 0505dbb
Last updated: Thu Nov 3 17:20 PDT 2022
View integration test log & download artifacts

Failures	Configs
firestore	[TEST] [FLAKINESS] [Android] [1/3 os: windows] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
functions	[TEST] [FLAKINESS] [Android] [1/3 os: windows] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
gma	[TEST] [FAILURE] [iOS] [macos] [1/2 ios_device: ios_target] (2 failed tests)   FirebaseGmaTest.TestRewardedAdLoadEmptyRequest   FirebaseGmaTest.TestRewardedAdStress [TEST] [FLAKINESS] [Android] [1/3 os: ubuntu] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
installations	[TEST] [FLAKINESS] [Android] [1/3 os: macos] [1/2 android_device: android_target] (1 failed tests)   FirebaseInstallationsTest.TestCanGetToken
messaging	[TEST] [FLAKINESS] [Android] [1/3 os: ubuntu] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT
storage	[TEST] [FLAKINESS] [Android] [2/3 os: windows ubuntu] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT

Add flaky tests to go/fpl-cpp-flake-tracker