Adjust generation scripts to explicitly choose the MSBuild engine

- ensure native assets are included in GenerateReferenceAssemblies.ps1 build
- clean up the global state that tools.ps1 corrupts

Author: dougbu

eng/scripts/GenerateProjectList.ps1

@@ -1,10 +1,18 @@
 param(
     [switch]$ci
 )
-$ErrorActionPreference = 'stop'
 
+$ErrorActionPreference = 'stop'
+$msbuildEngine = 'dotnet'
 $repoRoot = Resolve-Path "$PSScriptRoot/../.."
 
-& "$repoRoot\eng\common\msbuild.ps1" -ci:$ci "$repoRoot/eng/CodeGen.proj" `
+try {
+  & "$repoRoot\eng\common\msbuild.ps1" -ci:$ci "$repoRoot/eng/CodeGen.proj" `
     /t:GenerateProjectList `
     /bl:artifacts/log/genprojlist.binlog
+} finally {
+  Remove-Item variable:global:_BuildTool -ErrorAction Ignore
+  Remove-Item variable:global:_DotNetInstallDir -ErrorAction Ignore
+  Remove-Item variable:global:_ToolsetBuildProj -ErrorAction Ignore
+  Remove-Item variable:global:_MSBuildExe -ErrorAction Ignore
+}

eng/scripts/GenerateReferenceAssemblies.ps1

@@ -1,10 +1,26 @@
 param(
     [switch]$ci
 )
-$ErrorActionPreference = 'stop'
 
+$ErrorActionPreference = 'stop'
 $repoRoot = Resolve-Path "$PSScriptRoot/../.."
 
-& "$repoRoot\eng\common\msbuild.ps1" -ci:$ci "$repoRoot/eng/CodeGen.proj" `
+try {
+  # eng/common/msbuild.ps1 builds the Debug configuration unless there's a $Configuration variable. Match that here.
+  & "$repoRoot\build.ps1"  -ci:$ci -nobl -buildNative -configuration Debug
+
+  Remove-Item variable:global:_BuildTool -ErrorAction Ignore
+  Remove-Item variable:global:_DotNetInstallDir -ErrorAction Ignore
+  Remove-Item variable:global:_ToolsetBuildProj -ErrorAction Ignore
+  Remove-Item variable:global:_MSBuildExe -ErrorAction Ignore
+
+  $msbuildEngine = 'dotnet'
+  & "$repoRoot\eng\common\msbuild.ps1" -ci:$ci "$repoRoot/eng/CodeGen.proj" `
     /t:GenerateReferenceSources `
     /bl:artifacts/log/genrefassemblies.binlog
+} finally {
+  Remove-Item variable:global:_BuildTool -ErrorAction Ignore
+  Remove-Item variable:global:_DotNetInstallDir -ErrorAction Ignore
+  Remove-Item variable:global:_ToolsetBuildProj -ErrorAction Ignore
+  Remove-Item variable:global:_MSBuildExe -ErrorAction Ignore
+}