x64 macOS debugging under emulation broken by .NET 9

[gregg-miskelly]

Description

On .NET 9, it is no longer possible to debug the x64 runtime when it is running under emulation (Rosetta) on an arm64 macOS. The same scenario works with .NET 8.

Reproduction Steps

On an ARM64 macOS machine:

1. Install the ARM64 and x64 .NET SDK
2. Create a new console project targeting .NET 9
3. Configure the debugger to run the project in the x64 runtime instead of ARM64. Instructions for VS Code
4. Set a breakpoint on the first line of main
5. Launch the project

Expected behavior

The user's module should load and run in the target process

Actual behavior

The .NET Runtime fails to initialize when being debugged. The last callback sent is a thread create.

Regression?

This is a regression from .NET 8

Known Workarounds

None known

Configuration

OS: macOS ARM64 Sonoma
Runtime: macOS x64

Other information

No response

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[hoyosjs]

Dupe of #112156