Temporarily include libunwind.a from the NDK toolchain

MonoVM requires `libunwind.a` on x86_64.  Until the requirement is
removed, we'll include the archive.

dotnet/runtime#107615

Author: grendello

build-tools/create-packs/Microsoft.Android.Runtime.proj

@@ -54,6 +54,10 @@ projects that use the Microsoft.Android framework in .NET 6+.
       <_AndroidRuntimePackAssets Include="$(MicrosoftAndroidSdkOutDir)lib\$(AndroidRID)\crtbegin_so.o" />
       <_AndroidRuntimePackAssets Include="$(MicrosoftAndroidSdkOutDir)lib\$(AndroidRID)\crtend_so.o" />
       <_AndroidRuntimePackAssets Include="$(MicrosoftAndroidSdkOutDir)lib\$(AndroidRID)\libclang_rt.builtins-*-android.a" />
+
+      <!-- Remove once https://github.com/dotnet/runtime/pull/107615 is merged and released -->
+      <_AndroidRuntimePackAssets Include="$(MicrosoftAndroidSdkOutDir)lib\$(AndroidRID)\libunwind.a" />
+
       <FrameworkListFileClass Include="@(_AndroidRuntimePackAssemblies->'%(Filename)%(Extension)')" Profile="Android" />
       <FrameworkListFileClass Include="@(_AndroidRuntimePackAssets->'%(Filename)%(Extension)')" Profile="Android" />
     </ItemGroup>

build-tools/xaprepare/xaprepare/Steps/Step_Android_SDK_NDK.cs

@@ -197,9 +197,18 @@ bool CopyRedistributableFiles (Context context)
 					BuildAndroidPlatforms.NdkMinimumAPI.ToString (CultureInfo.InvariantCulture)
 				);
 
+				string clangArch = Configurables.Defaults.AbiToClangArch[abi];
 				CopyFile (abi, crtFilesPath, "crtbegin_so.o");
 				CopyFile (abi, crtFilesPath, "crtend_so.o");
-				CopyFile (abi, clangLibPath, $"libclang_rt.builtins-{Configurables.Defaults.AbiToClangArch[abi]}-android.a");
+				CopyFile (abi, clangLibPath, $"libclang_rt.builtins-{clangArch}-android.a");
+
+				// Yay, consistency
+				if (String.Compare (clangArch, "i686", StringComparison.Ordinal) == 0) {
+					clangArch = "i386";
+				}
+
+				// Remove once https://github.com/dotnet/runtime/pull/107615 is merged and released
+				CopyFile (abi, Path.Combine (clangLibPath, clangArch), "libunwind.a");
 			}
 
 			return true;

src/Xamarin.Android.Build.Tasks/Utilities/NativeRuntimeComponents.cs

@@ -102,6 +102,11 @@ public NativeRuntimeComponents (ITaskItem[] monoComponents)
 			new ClangBuiltinsArchive ("arm"),
 			new ClangBuiltinsArchive ("i686"),
 			new ClangBuiltinsArchive ("x86_64"),
+
+			// Remove once https://github.com/dotnet/runtime/pull/107615 is merged and released
+			new Archive ("libunwind.a") {
+				DontExportSymbols = true,
+			},
 		};
 
 		// Just the base names of libraries to link into the unified runtime.  Must have all the dependencies of all the static archives we