[tools] Pass the AOTCompiler property to the ComputeAOTArguments linker steps.

So that the ComputeAOTArguments can compute the llvm-path value to pass to the AOT
compiler (the llvm-path value states where the opt and llc command-line tools are,
and they're next to the AOT compiler).

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -356,6 +356,7 @@
 
 			<_CustomLinkerOptions>
 				AssemblyName=$(AssemblyName).dll
+				AOTCompiler=$(_AOTCompiler)
 				AOTOutputDirectory=$(_AOTOutputDirectory)
 				CacheDirectory=$(_LinkerCacheDirectory)
 				Debug=$(_BundlerDebug)

tools/common/Application.cs

@@ -1408,7 +1408,7 @@ namespace Xamarin.Bundler {
 			return processArguments;
 		}
 
-		public void GetAotArguments (string filename, Abi abi, string outputDir, string outputFile, string llvmOutputFile, string dataFile, out List<string> processArguments, out List<string> aotArguments)
+		public void GetAotArguments (string filename, Abi abi, string outputDir, string outputFile, string llvmOutputFile, string dataFile, out List<string> processArguments, out List<string> aotArguments, string llvm_path = null)
 		{
 			string fname = Path.GetFileName (filename);
 			processArguments = new List<string> ();
@@ -1472,8 +1472,13 @@ namespace Xamarin.Bundler {
 				aotArguments.Add ($"msym-dir={msymdir}");
 			}
 
-			if (enable_llvm)
-				aotArguments.Add ($"llvm-path={Driver.GetFrameworkCurrentDirectory (app)}/LLVM/bin/");
+			if (enable_llvm) {
+				if (!string.IsNullOrEmpty (llvm_path)) {
+					aotArguments.Add ($"llvm-path={llvm_path}");
+				} else {
+					aotArguments.Add ($"llvm-path={Driver.GetFrameworkCurrentDirectory (app)}/LLVM/bin/");
+				}
+			}
 
 			aotArguments.Add ($"outfile={outputFile}");
 			if (enable_llvm)

tools/dotnet-linker/LinkerConfiguration.cs

@@ -17,6 +17,7 @@ using ObjCRuntime;
 namespace Xamarin.Linker {
 	public class LinkerConfiguration {
 		public List<Abi> Abis;
+		public string AOTCompiler;
 		public string AOTOutputDirectory;
 		public string CacheDirectory { get; private set; }
 		public Version DeploymentTarget { get; private set; }
@@ -104,6 +105,9 @@ namespace Xamarin.Linker {
 					// This is the AssemblyName MSBuild property for the main project (which is also the root/entry assembly)
 					Application.RootAssemblies.Add (value);
 					break;
+				case "AOTCompiler":
+					AOTCompiler = value;
+					break;
 				case "AOTOutputDirectory":
 					AOTOutputDirectory = value;
 					break;

tools/dotnet-linker/Steps/ComputeAOTArguments.cs

@@ -39,7 +39,7 @@ namespace Xamarin.Linker {
 					var llvmFile = string.Empty;
 					if ((abi & Abi.LLVM) == Abi.LLVM)
 						throw ErrorHelper.CreateError (99, $"Support for LLVM hasn't been implemented yet.");
-					app.GetAotArguments (asm.FullPath, abi, outputDirectory, aotAssembly, llvmFile, aotData, out var processArguments, out var aotArguments);
+					app.GetAotArguments (asm.FullPath, abi, outputDirectory, aotAssembly, llvmFile, aotData, out var processArguments, out var aotArguments, Path.GetDirectoryName (Configuration.AOTCompiler));
 					item.Metadata.Add ("Arguments", StringUtils.FormatArguments (aotArguments));
 					item.Metadata.Add ("ProcessArguments", StringUtils.FormatArguments (processArguments));
 					item.Metadata.Add ("Abi", abiString);