base: cmdIsThreadAlive implementation

Some GDB implementations, specifically ARM's, needed this to be able to
switch between thread.

Change-Id: I0d4db0c008c336eac51008bcfefd04c375c333f7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63527
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed