arch: Make the decoder takeOverFrom method virtual.

This is only implemented for x86. It's called very rarely, and so
virtual function overhead is practically irrelevant.

Change-Id: Ib6e05a903df95b801164e44d1662e130419fdbd8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52076
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Earl Ou <shunhsingou@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
7 files changed