Enable Apple Silicon SDK builds

[sdmaclea]

Enable Apple Silicon SDK builds

• Add macos arm64 to readme
• Enable osx-arm64 builds
• Use vmImage: 'macOS-10.15'

Fixes #8840

The Apple Silicon build is likely to be unstable for general usage. Known issues.

• Runtime hasn't fully implemented the Apple Silicon ABI. This means interop with native C is not working. It may affect lots of areas. One known area is in the call to fork a process
• The runtime is missing the FlushProcessWriteBuffers changes needed for Apple Silicon. This means there could be GC issues
• The runtime stack probing code doesn't support 16k pages
• The ASP.NET runtime doesn't have native binaries for Apple Silicon. Some scenarios will not work yet.

[sdmaclea]

@janvorli This is my draft for the osx-arm64 SDK.

I have a few hacks at the moment:

• I have disabled aspnetcore download
• I have not marked aspnetcore as supported
• I have disabled building the macos installer. I can't seem to figure out why some of the *osx-arm64.pkg files are missing.

I haven't tried the resulting SDK tgz yet, but I thought it would help us understand how important the interop issues were going to be to the SDK.

I have it left as draft because the workarounds are intended to be temporary.

/cc @mangod9 @sandreenko

[sdmaclea]

I haven't tested them yet, but they are built:

artifacts/packages/Release/NonShipping/dotnet-sdk-internal-6.0.100-ci-osx-arm64.tar.gz
artifacts/packages/Release/Shipping/dotnet-sdk-6.0.100-ci-osx-arm64.tar.gz

[sdmaclea]

Still needs work Note seg fault below. I'll take a look next week.

$dotnet-sdk/dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.100-ci
 Commit:    23dc3eb5b2

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  11.0
 OS Platform: Darwin
 RID:         osx.11.0-arm64
 Base Path:   /Users/steve/dotnet-sdk/sdk/6.0.100-ci/

Host (useful for support):
  Version: 6.0.0-alpha.1.20513.9
  Commit:  eea2256e56

.NET SDKs installed:
  6.0.100-ci [/Users/steve/dotnet-sdk/sdk]

.NET runtimes installed:
  Microsoft.NETCore.App 6.0.0-alpha.1.20513.9 [/Users/steve/dotnet-sdk/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

$dotnet-sdk/dotnet new console -o nc

Welcome to .NET 6.0!
---------------------
SDK Version: 6.0.100-ci

Telemetry
---------
The .NET tools collect usage data in order to help us improve your experience. It is collected by Microsoft and shared with the community. You can opt-out of telemetry by setting the DOTNET_CLI_TELEMETRY_OPTOUT environment variable to '1' or 'true' using your favorite shell.

Read more about .NET CLI Tools telemetry: https://aka.ms/dotnet-cli-telemetry

----------------
Installed an ASP.NET Core HTTPS development certificate.
To trust the certificate run 'dotnet dev-certs https --trust' (Windows and macOS only).
Learn about HTTPS: https://aka.ms/dotnet-https
----------------
Write your first app: https://aka.ms/dotnet-hello-world
Find out what's new: https://aka.ms/dotnet-whats-new
Explore documentation: https://aka.ms/dotnet-docs
Report issues and find source on GitHub: https://github.com/dotnet/core
Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli
--------------------------------------------------------------------------------------
zsh: segmentation fault  dotnet-sdk/dotnet new console -o nc

[sdmaclea]

This is closer.

• 864c314 Will need to be removed when [master] Update dependencies from dotnet/aspnetcore sdk#14338 merges and is integrated in installer. (Marked as draft because of this). I removed this in fe7815f below, because it was causing the other legs to fail.
• I am using the osx-x64 netstandard-targeting-pack pkg. This should be OK as the osx-arm64 targeting pack is just an archive with reference assemblies and runtime independent manifexts.
• I removed the updates to the readme for osx-x64. These had a merge conflict and I wanted to merge them separately.

[sdmaclea]

Blocked on #9064

[mangod9]

#9064 has now merged.

[sdmaclea]

This should build successfully and is ready for review.

[mangod9]

LGTM

[hoyosjs]

@sfoslund can you please review here? I would like to have a repo maintainer confirm this looks correct.

[mangod9]

Is this good to merge?

[sfoslund]

Sorry for the delay, looks good to me

[sdmaclea]

I have updated the top post with known issues, just so expectation are not completely uncalibrated.

[sdmaclea]

Thanks @sfoslund