stdlib: Add additional warns when `get_runtime_isa` used

While the `runtime` module's `get_runtime_isa` function throws a warning
to remind user's the function is deprecated, this was not always helpful
to a user when setting a processor without a target ISA.

This change adds additional warnings to the SimpleSwitchableProcessor
and the SimpleProcessor. These warnings explain not explicitly setting
the ISA via the processor's constructor is deprecated behavior.

Change-Id: I994ad8355e0d1c3f07374bebe2b59106fb04d212
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63331
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed