Add a test for determinism

Resolves dotnet#73931. This checks that the result of parallel build is the same as the result of single-threaded build.

I'd like to add some more code to this so that there's more junk to compile but don't have a good idea of what to add. `XmlSerializer`? Suggestions welcome.

src/tests/nativeaot/SmokeTests/Determinism/Determinism.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+
+using var baseline = File.OpenRead("baseline.object");
+using var compare = File.OpenRead("compare.object");
+
+Console.WriteLine($"Baseline size: {baseline.Length}");
+Console.WriteLine($"Compare size: {compare.Length}");
+
+if (baseline.Length != compare.Length)
+    throw new Exception("Different sizes");
+
+for (int i = 0; i < baseline.Length; i++)
+{
+    if (baseline.ReadByte() != compare.ReadByte())
+        throw new Exception($"Different at byte {i}");
+}
+
+return 100;

src/tests/nativeaot/SmokeTests/Determinism/Determinism.csproj

@@ -0,0 +1,37 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <CLRTestPriority>0</CLRTestPriority>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Determinism.cs" />
+  </ItemGroup>
+
+  <Target Name="IlcCompileSingleThreaded"
+      Inputs="$(NativeIntermediateOutputPath)%(ManagedBinary.Filename)$(IlcOutputFileExt)"
+      Outputs="$(NativeIntermediateOutputPath)%(ManagedBinary.Filename)$(IlcOutputFileExt)-singlethreaded"
+      AfterTargets="IlcCompile">
+
+    <PropertyGroup>
+      <OldObjectFileName>$(NativeIntermediateOutputPath)%(ManagedBinary.Filename)$(IlcOutputFileExt)</OldObjectFileName>
+      <NewObjectFileName>$(NativeIntermediateOutputPath)%(ManagedBinary.Filename)$(IlcOutputFileExt)-singlethreaded</NewObjectFileName>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <IlcArg Remove="-o:$(OldObjectFileName)" />
+      <IlcArg Include="-o:$(NewObjectFileName)" />
+      <IlcArg Include="--parallelism:1" />
+    </ItemGroup>
+
+    <WriteLinesToFile File="%(ManagedBinary.IlcRspFile)-singlethreaded" Lines="@(IlcArg)" Overwrite="true" WriteOnlyWhenDifferent="true" />
+
+    <Message Text="Compiling single-threaded baseline" Importance="High" />
+
+    <Exec Command="&quot;$(IlcToolsPath)\ilc&quot; @&quot;%(ManagedBinary.IlcRspFile)-singlethreaded&quot;"
+          EnvironmentVariables="$(_IlcEnvironmentVariables)" />
+
+    <Copy SourceFiles="$(OldObjectFileName)" DestinationFiles="$(OutDir)\baseline.object" />
+    <Copy SourceFiles="$(NewObjectFileName)" DestinationFiles="$(OutDir)\compare.object" />
+  </Target>
+</Project>