VS_DOTNET_PLATFORM to overwrite the "platform" for a C# target

For example, you can now create a AnyCPU target by using
set_property(TARGET Example PROPERTY VS_DOTNET_PLATFORM "AnyCPU")

Source/cmVisualStudio10TargetGenerator.cxx

@@ -93,7 +93,16 @@ cmVisualStudio10TargetGenerator::cmVisualStudio10TargetGenerator(
     (cmLocalVisualStudio7Generator*)this->GeneratorTarget->GetLocalGenerator();
   this->Name = this->GeneratorTarget->GetName();
   this->GUID = this->GlobalGenerator->GetGUID(this->Name);
-  this->Platform = gg->GetPlatformName();
+
+  // overwrite the PLATFORM if required - Only for Managed code
+  const char* vsdotnetplatform =
+    this->GeneratorTarget->GetProperty("VS_DOTNET_PLATFORM");
+  if (this->Managed && vsdotnetplatform) {
+    this->Platform = vsdotnetplatform;
+  } else {
+    this->Platform = gg->GetPlatformName();
+  }
+
   this->NsightTegra = gg->IsNsightTegra();
   for (int i = 0; i < 4; ++i) {
     this->NsightTegraVersion[i] = 0;