Enable PlatformNativeR2R test on macOS

[elinor-fung]

• Allow setting Crossgen2OutputFormat in tests - passed as -f <format> to crossgen2
• Update generated test scripts to handle Mach-O output format for crossgen2, linking the produced object into a dynamic library
• Enable PlatformNativeR2R test on macOS and set format to macho

cc @dotnet/appmodel @AaronRobinsonMSFT

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[am11]

Will it be exercised with /azp run runtime-coreclr crossgen2 or /azp run runtime-ioslike?

[elinor-fung]

It should actually be part of the regular run (and actually test R2R since it has AlwaysUseCrossgen2=true). The console log from this PR shows the PlatformNativeR2R test being crossgen-ed and run.

[Copilot]

Pull Request Overview

This PR enables the PlatformNativeR2R test on macOS by adding support for Mach-O output format in crossgen2 compilation. The changes introduce a CrossGen2OutputFormat property that can be passed to crossgen2, update the test generation scripts to handle Mach-O object files and link them into dynamic libraries, and enable the previously disabled test on macOS and Apple mobile platforms.

Key Changes:

• Added CrossGen2OutputFormat property support in test project configuration
• Updated bash script generation to handle Mach-O format output, including linking .o files into .dylib libraries
• Enabled PlatformNativeR2R test for Windows, macOS, and Apple mobile platforms (previously Windows-only)

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/tests/Loader/PlatformNativeR2R/PlatformNativeR2R.csproj	Removes Windows-only restriction, updates platform condition to include macOS/Apple targets, and sets CrossGen2OutputFormat to macho
src/tests/Loader/PlatformNativeR2R/PlatformNativeR2R.cs	Enables previously commented-out assertion for READYTORUN_FLAG_PlatformNativeImage
src/tests/Common/CLRTest.CrossGen.targets	Adds support for CrossGen2OutputFormat parameter, implements Mach-O linking logic with clang, updates file extension handling for composite builds, and cleans up composite-r2r files with wildcard pattern

[AaronRobinsonMSFT]

💩