[Xamarin.Android.Build.Tasks]: Fix incremental builds (#10)

The (poorly named) `_Foo` target didn't have any `//Target/@Inputs`
or `//Target/@Outputs` attribute values, and thus would constantly:

1. Re-execute on every build, which would
2. Create a "new" $(IntermediateOutputPath)Profile.g.cs, which would
3. Require that Mono.Android.dll be rebuilt, as a file had changed.

Rename the `_Foo` target to `_GenerateProfileClass`, and add `Inputs`
and `Outputs` attributes so that the target isn't constantly executed.

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.targets

@@ -1,16 +1,18 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="Xamarin.Android.Tools.BootstrapTasks.GenerateProfile" AssemblyFile="..\..\bin\Build$(Configuration)\Xamarin.Android.Tools.BootstrapTasks.dll" />
- <Target Name="_Foo" BeforeTargets="CoreCompile">
- <PropertyGroup>
- <_GeneratedProfileClass>$(IntermediateOutputPath)Profile.g.cs</_GeneratedProfileClass>
- </PropertyGroup>
- <ItemGroup>
- <SharedRuntimeBuildPath Include="..\..\bin\$(Configuration)\lib\xbuild-frameworks\MonoAndroid\" />
- </ItemGroup>
- <CreateItem Include="@(SharedRuntimeBuildPath->'%(Identity)\\v1.0\*.dll');@(SharedRuntimeBuildPath->'%(Identity)\\v6.0\*.dll')">
- <Output TaskParameter="Include" ItemName="_SharedRuntimeAssemblies" />
- </CreateItem>
+ <PropertyGroup>
+ <_SharedRuntimeBuildPath>..\..\bin\$(Configuration)\lib\xbuild-frameworks\MonoAndroid\</_SharedRuntimeBuildPath>
+ <_GeneratedProfileClass>$(IntermediateOutputPath)Profile.g.cs</_GeneratedProfileClass>
+ </PropertyGroup>
+ <ItemGroup>
+ <_SharedRuntimeAssemblies Include="$(_SharedRuntimeBuildPath)v1.0\*.dll;$(_SharedRuntimeBuildPath)$(AndroidFrameworkVersion)\*.dll"/>
+ </ItemGroup>
+
+ <Target Name="_GenerateProfileClass" BeforeTargets="CoreCompile"
+ Inputs="@(_SharedRuntimeAssemblies)"
+ Outputs="$(_GeneratedProfileClass)"
+ >
  <GenerateProfile Files="@(_SharedRuntimeAssemblies)" OutputFile="$(_GeneratedProfileClass)" />
  <ItemGroup>
  <Compile Include="$(_GeneratedProfileClass)" />
@@ -20,4 +22,4 @@
  Lines="$(_GeneratedProfileClass)"
  Overwrite="false"/>
  </Target>
-</Project>
+</Project>