In ARM64, fallback to ARM32/x86 if SDK installer is not found

[carlossanlop]

Related to: dotnet/roslyn-analyzers#3933

If the architecture is arm64, but the dotnet-install script does not find an SDK installer for that architecture, fallback to arm32. And if no arm32 SDK installer is found, fallback to x86.

Here is the output of build.cmd from the roslyn-analyzers repo, when executed from my ARM64 machine:

C:\User\carlos\source\repos\roslyn-analyzers ❯ .\Build.cmd
dotnet-install: Downloading link: https://dotnetcli.azureedge.net/dotnet/Sdk/3.1.200/dotnet-sdk-3.1.200-win-arm64.zip
dotnet-install: Cannot download: https://dotnetcli.azureedge.net/dotnet/Sdk/3.1.200/dotnet-sdk-3.1.200-win-arm64.zip
dotnet-install: Downloading legacy link: https://dotnetcli.azureedge.net/dotnet/Sdk/3.1.200/dotnet-dev-win-arm64.3.1.200.zip
dotnet-install: Cannot download: https://dotnetcli.azureedge.net/dotnet/Sdk/3.1.200/dotnet-dev-win-arm64.3.1.200.zip
Failed to install dotnet runtime '' from public location.

The ARM64 SDK installer does not exist for 3.1.

So I had to hardcode the $architecture = '' argument to x86 in the script that attempts the installation, so that I could get a successful compilation:

roslyn-analyzers/eng/common/tools.ps1#L223-L225
From:

 function InstallDotNetSdk([string] $dotnetRoot, [string] $version, [string] $architecture = '') { 
   InstallDotNet $dotnetRoot $version $architecture 
 }

To:

 function InstallDotNetSdk([string] $dotnetRoot, [string] $version, [string] $architecture = 'x86') { 
   InstallDotNet $dotnetRoot $version x86
 }

cc @jmarolf

[garath]

Arcade avoids making these kinds of assumptions. It would be better aligned if we looked at plumbing these parameters further up so that build logic can configure them properly (instead of requiring edits to managed files). Would that be an acceptable solution for you?