loader: Fix MSVC post-build event so copy with non-existent dir works
loader: Fix MSVC post-build event so copy with non-existent dir works

Change-Id: I4629b36c1fbde76ba025fa38937dfcd22bbd9157

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools