Don't modify LOCAL_CHECKED_MODULE.

Use a temporary variable my_checked_module instead,
so that we don't override the 2nd_arch's checked module with the
1st_arch's in multilib build.
Note that by default we checkbuild 2nd_arch only for host modules,
but not for target modules.
We enable multlib for target modules by default, it would take too
much time to checkbuild for both archs. For 32-bit modules actually we
can checkbuild a 32-bit product.

Change-Id: I0a5ba75699225b7641442673483731a8fd360d61