Ensure that iOS builds get correct library identity for native libraries

[filipnavara]

Fixes #34637

I am not 100% sure this is the right place to put it. The otool -L output now looks like this:

otool -L /Users/filipnavara/Projects/runtime/artifacts/bin/native/net6.0-iOS-Debug-x64/./libSystem.IO.Compression.Native.dylib
/Users/filipnavara/Projects/runtime/artifacts/bin/native/net6.0-iOS-Debug-x64/./libSystem.IO.Compression.Native.dylib:
	@rpath/libSystem.IO.Compression.Native.dylib (compatibility version 0.0.0, current version 0.0.0)
	/usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.11)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1292.0.0)

/cc @akoeplinger @rolfbjarne

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[akoeplinger]

LGTM, thanks!

[akoeplinger]

Looks like the iOS arm64 build fails with:

##[error]ld(0,0): error : (NETCORE_ENGINEERING_TELEMETRY=Build) embedded dylibs/frameworks only run on iOS 8 or later

We're indeed targetting iOS 7 for device builds and iOS 8 for simulator. @rolfbjarne do you know what this error means, should we use @executable_path instead?

[filipnavara]

That's quite unfortunate. I think Xamarin itself uses @rpath but it does it through install_name_tool and not the linker. That may simply behave differently and ignore the iOS version. It also seems that @rpath actually worked on iOS 7 but it was not officially supported.

[filipnavara]

Hm, @executable_path fails with the exact same error.

[akoeplinger]

Looks like this is usually a warning instead of an error but we're using warnings-as-errors so this gets turned into an error.

[akoeplinger]

We discussed on Discord and iOS 8 is fine as the minimum version these days.

[rolfbjarne]

We discussed on Discord and iOS 8 is fine as the minimum version these days.

8.0 as the minimum version is fine for dynamic libraries or frameworks, it's not for static libraries, since we still support iOS 7.

We're indeed targetting iOS 7 for device builds and iOS 8 for simulator.

Apple is dropping support for older simulators quite aggressively, so there's not much purpose in building for a simulator you can never use. On the other hand it's still possible to build for older device versions in Xcode.