stdlib: Update the default exit events and warning

This change updates the default actions taken when the user doesn't
specify generators for the exit events in the simulator. Rather than
defining default generators, this change makes the generators more
generic and gives a new decorator to mark them as default.

This change then updates the default generators in the simulator and
only makes some of them issue a default warning. For exit events such as
EXIT, the default will no longer print a warning.

Change-Id: I5552f52392f3aea577034ed278a9ff9e8b5b0b01
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64251
Reviewed-by: Zhantong Qiu <ztqiu@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed