[nativeaot] fix project builds on Windows (#9710)

In 2fa7954, we got Android projects *building* for NativeAOT.
However, this didn't work at all on Windows.

Reviewing how NativeAOT's MSBuild targets are setup, they expect
various tooling to be available in `%PATH%`.

To fix this:

* Create a new `<SetNdkPathForIlc/>` MSBuild task.

* That simply sets the Android NDK "bin" directory to `%PATH%`.

NativeAOT apps now successfully build (and run) on Windows. I also
updated an integration test to verify this.

Unfortunately, we still have to set `$(DisableUnsupportedError)` or we
will get the message:

    D:\.nuget\packages\microsoft.dotnet.ilcompiler\10.0.0-alpha.1.25067.10\build\Microsoft.NETCore.Native.Publish.targets(61,5):
    error : Cross-OS native compilation is not supported. Please use the appropriate OS-specific target.

A future change might be needed here, or it might be fine to for the
Android workload to set this property:

* https://github.com/dotnet/runtime/blob/ea4a404ef8890f265780f798e7668d4710259e03/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.Publish.targets#L61-L62

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.NativeAOT.targets

@@ -7,9 +7,13 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
 -->
 <Project>
 
+  <UsingTask TaskName="Xamarin.Android.Tasks.SetNdkPathForIlc" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
+
   <!-- Default property values for NativeAOT -->
   <PropertyGroup>
     <_AndroidRuntimePackRuntime>NativeAOT</_AndroidRuntimePackRuntime>
+    <!-- NativeAOT's targets currently gives an error about cross-compilation -->
+    <DisableUnsupportedError Condition=" $([MSBuild]::IsOSPlatform('windows')) and '$(DisableUnsupportedError)' == '' ">true</DisableUnsupportedError>
   </PropertyGroup>
 
   <!-- Make IlcCompile depend on the trimmer -->
@@ -32,16 +36,14 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
     <PropertyGroup>
       <_NdkAbi Condition=" '$(RuntimeIdentifier)' == 'android-arm64' ">aarch64</_NdkAbi>
       <_NdkAbi Condition=" '$(RuntimeIdentifier)' == 'android-x64' ">x86_64</_NdkAbi>
-      <_NdkSysrootAbi>$(_NdkAbi)-linux-android</_NdkSysrootAbi>      
-      <_NdkClangPrefix>$(_NdkAbi)-linux-android21-</_NdkClangPrefix>
+      <_NdkSysrootAbi>$(_NdkAbi)-linux-android</_NdkSysrootAbi>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('windows')) ">windows-x86_64</_NdkPrebuiltAbi>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('osx')) ">darwin-x86_64</_NdkPrebuiltAbi>
       <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('linux')) ">linux-x86_64</_NdkPrebuiltAbi>
       <_NdkSysrootDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/sysroot/usr/lib/$(_NdkSysrootAbi)/</_NdkSysrootDir>
       <_NdkBinDir>$(_AndroidNdkDirectory)toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/bin/</_NdkBinDir>
-      <CppCompilerAndLinker>$(_NdkBinDir)$(_NdkClangPrefix)clang++</CppCompilerAndLinker>
-      <CppLinker>$(CppCompilerAndLinker)</CppLinker>
-      <ObjCopyName>$(_NdkBinDir)llvm-objcopy</ObjCopyName>
+      <CppCompilerAndLinker>clang++</CppCompilerAndLinker>
+      <ObjCopyName>llvm-objcopy</ObjCopyName>
 
       <!-- Example settings from: https://github.com/xamarin/xamarin-macios/blob/c43d4ea40bc777969e3b158cf46446df292d8449/dotnet/targets/Xamarin.Shared.Sdk.targets#L541-L550 -->
       <RunILLink>true</RunILLink>
@@ -66,6 +68,8 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
       <!-- HACK: prevents: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "__start___modules" -->
       <LinkerFlavor Condition=" '$(LinkerFlavor)' == '' ">lld</LinkerFlavor>
     </PropertyGroup>
+
+    <SetNdkPathForIlc NdkBinDirectory="$(_NdkBinDir)" />
   </Target>
 
   <Target Name="_AndroidComputeIlcCompileInputs">

src/Xamarin.Android.Build.Tasks/Tasks/SetNdkPathForIlc.cs

@@ -0,0 +1,27 @@
+using System;
+using System.IO;
+using Microsoft.Android.Build.Tasks;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Xamarin.Android.Tasks;
+
+/// <summary>
+/// NativeAOT's compiler (ILC) expects to find tooling in $PATH
+/// </summary>
+public class SetNdkPathForIlc : AndroidTask
+{
+	public override string TaskPrefix => "SILC";
+
+	[Required]
+	public string NdkBinDirectory { get; set; } = "";
+
+	public override bool RunTask ()
+	{
+		var ndkbin = Path.GetFullPath (NdkBinDirectory);
+		var path = $"{ndkbin}{Path.PathSeparator}{Environment.GetEnvironmentVariable ("PATH")}";
+		Log.LogDebugMessage ($"Setting $PATH to: {path}");
+		Environment.SetEnvironmentVariable ("PATH", path);
+		return !Log.HasLoggedErrors;
+	}
+}

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest2.cs

@@ -108,12 +108,6 @@ public void BuildBasicApplication ([Values (true, false)] bool isRelease, [Value
 		[Test]
 		public void NativeAOT ()
 		{
-			if (IsWindows) {
-				// Microsoft.NETCore.Native.Publish.targets(61,5): Cross-OS native compilation is not supported.
-				// Set $(DisableUnsupportedError)=true, Microsoft.NETCore.Native.Unix.targets(296,5): error : Platform linker ('C:\Android\android-sdk\ndk\26.3.11579264\toolchains/llvm/prebuilt/windows-x86_64/bin/aarch64-linux-android21-clang++' or 'gcc') not found in PATH. Ensure you have all the required prerequisites documented at https://aka.ms/nativeaot-prerequisites.
-				Assert.Ignore ("This test is not valid on Windows.");
-			}
-
 			var proj = new XamarinAndroidApplicationProject {
 				ProjectName = "Hello",
 				IsRelease = true,