Find custom.props in parent dir (#4946)

* Update LkgToolset.props

Fix build break - custom.props in parent directory

* Update LkgToolset.props

Author: Scottj1s

LkgToolset.props

@@ -13,8 +13,9 @@
   <PropertyGroup Condition="'$(Platform)'=='x86'">
     <WorkaroundLkgWin32>true</WorkaroundLkgWin32>
     <Platform>Win32</Platform>
+    <CustomProps>$([MSBuild]::GetPathOfFileAbove('custom.props', '$(MSBuildThisFileDirectory)'))</CustomProps>
   </PropertyGroup>
-  <Import Project="custom.props" Condition="Exists('custom.props') and '$(WorkaroundLkgWin32)'=='true'" />
+  <Import Project="$(CustomProps)" Condition="Exists('$(CustomProps)') and '$(WorkaroundLkgWin32)'=='true'" />
   <PropertyGroup Condition="'$(WorkaroundLkgWin32)'=='true'">
     <Platform>x86</Platform>
   </PropertyGroup>