Add mergeable libraries support to dynamic libraries

[denrase]

📜 Description

• Add make_mergable linker flags to supported SDKs

From the ld manual:

man ld | col -b | open -tf

Mergeable Library Options
 -make_mergeable
     Adds additional metadata to a dylib which makes it a mergeable
     library.  It can still be used as a dylib, or can be merged into
     other binaries when they link it with a -merge* option.

Also, users have to build with Xcode >= 15.

When you include your mergeable library in an XCFramework, Xcode adds the key MergeableMetadata to the XCFramework’s Info.plist file to indicate to other projects that your library in the XCFramework is mergeable. You can only use XCFrameworks with mergeable metadata in Xcode 15 and later; in earlier versions, Xcode returns a build error.

💡 Motivation and Context

Users can enable mergable libraries featue for dynamic sentry frameworks.

See https://developer.apple.com/documentation/xcode/configuring-your-project-to-use-mergeable-libraries for more info.

💚 How did you test it?

Closes #3719

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

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[denrase]

Created a new PR which only enables mergeable libraries for the xcframeworks we build for SPM usage. (See #4367 for more info)

Reasons:

• Setting -Wl,-make_mergeable in the SDK.xcconfig has the side effect that no CI using Xcode < 15 is working anymore.

So we'd need to bump all CI to at least macos-14 and Xcode 15.2. Building with fastlane only worked with macos-14 and Xcode 16.

• Setting the MERGEABLE_LIBRARY key instead results in failed watchOS builds, even if set to no.

error: Mergeable libraries are not supported for architecture 'armv7k', but MERGEABLE_LIBRARY is assigned at level: project-xcconfig. (in target 'Sentry' from project 'Sentry')

Conditionals are not supported, and we cannot create xcconfig files based on platform.

So this is the least invasive way to add support for mergeable libraries. Still there's the large caviat that users need to use Xcode >= 15, so we need to consider this before merging.

[brustolin]

Thanks @denrase, LGTM