Disable multilevel lookup during build (#4367)

run.ps1

@@ -5,6 +5,9 @@ $restorePackagesPath = Join-Path $PSScriptRoot "packages"
 # We do not want to run the first-time experience.
 $env:DOTNET_SKIP_FIRST_TIME_EXPERIENCE = 1
 
+# Don't resolve runtime, shared framework, or SDK from other locations to ensure build determinism
+$env:DOTNET_MULTILEVEL_LOOKUP=0
+
 $initTools = Join-Path $PSScriptRoot "init-tools.cmd"
 & $initTools
 

run.sh

@@ -5,6 +5,9 @@ __scriptpath=$(cd "$(dirname "$0")"; pwd -P)
 # We do not want to run the first-time experience.
 export DOTNET_SKIP_FIRST_TIME_EXPERIENCE=1
 
+# Don't resolve runtime, shared framework, or SDK from other locations to ensure build determinism 
+export DOTNET_MULTILEVEL_LOOKUP=0
+
 # Source the init-tools.sh script rather than execute in order to preserve ulimit values in child-processes. https://github.com/dotnet/corefx/issues/19152
 . $__scriptpath/init-tools.sh
 

src/test/HostActivationTests/GivenThatICareAboutDotnetArgValidationScenarios.cs

@@ -94,7 +94,7 @@ namespace Microsoft.DotNet.CoreSetup.Test.HostActivation.ArgValidation
             dotnet.Exec("--fx-version")
                 .CaptureStdOut()
                 .CaptureStdErr()
-                .Execute()
+                .Execute(fExpectedToFail: true)
                 .Should()
                 .Fail()
                 .And