Fix for building on macOS

* Set execute bit on AOT compilers
* Use `%(FullPath)` where appropriate

Author: jonathanpeppers

build-tools/create-packs/Directory.Build.targets

@@ -119,6 +119,7 @@
     <Copy SourceFiles="@(_WLTemplates)" DestinationFolder="$(DotNetPreviewPath)template-packs" />
     <ItemGroup>
       <_UnixExecutables Include="$(DotNetPreviewPath)packs\Microsoft.Android.Sdk.*\*\tools\$(HostOS)\**\*.*" />
+      <_UnixExecutables Include="$(DotNetPreviewPath)packs\microsoft.netcore.app.runtime.aot.*.cross.*\*\tools\*.*" />
       <_FilesToTouch Include="$(DotNetPreviewPath)sdk-manifests\$(DotNetPreviewVersionBand)\Microsoft.NET.Workload.Android\**" />
       <_FilesToTouch Include="$(DotNetPreviewPath)packs\$([System.String]::Copy('%(_WLPacks.Filename)').Replace('.$(_WLPackVersion)', ''))\$(_WLPackVersion)\**" />
       <_FilesToTouch Include="$(DotNetPreviewPath)packs\$([System.String]::Copy('%(_AotPacks.Filename)').Replace('.$(MonoAOTCompilerVersion)', ''))\$(MonoAOTCompilerVersion)\**" />

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

@@ -27,13 +27,14 @@ For <MonoAOTCompiler/> usage, see:
     -->
     <ItemGroup>
       <_AotRuntimeIdentifiers Include="$([System.String]::Copy('%(_RIDs.Identity)').Replace('.21', ''))" />
+      <_AotCompilerPaths Include="$(MSBuildThisFileDirectory)..\..\..\microsoft.netcore.app.runtime.aot.osx-x64.cross.%(_AotRuntimeIdentifiers.Identity)\$(MonoAOTCompilerVersion)\tools\mono-aot-cross" />
     </ItemGroup>
     <MonoAOTCompiler
         AotModulesTableLanguage="$(_AotModulesTableLanguage)"
         AotModulesTablePath="$(_AotModulesTablePath)"
         AotProfilePath="$(_AotProfilePath)"
-        Assemblies="@(_ShrunkAssemblies)"
-        CompilerBinaryPath="$(MSBuildThisFileDirectory)..\..\..\microsoft.netcore.app.runtime.aot.osx-x64.cross.%(_AotRuntimeIdentifiers.Identity)\$(MonoAOTCompilerVersion)\tools\mono-aot-cross"
+        Assemblies="@(_ShrunkAssemblies->'%(FullPath)')"
+        CompilerBinaryPath="%(_AotCompilerPaths.FullPath)"
         DisableParallelAot="$(_DisableParallelAot)"
         LLVMPath="$(_LLVMPath)"
         Mode="$(AndroidAotMode)"