base: Add missing headers in extensible.hh

Add missing headers <cassert> and <type_traits> in extensible.hh

Change-Id: I01e49c62619383ea4f7da668ceaefe4a41418cd8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69480
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
1 file changed