tests: Fix failing SST and SystemC nightly tests

There was a bug with the SST and SystemC tests where they wouldn't
compile due to a missing path for the gdbremote/signals.hh
header, and this change includes that so they run properly.

Change-Id: I9ff0404e327358fe2d1b77388bbcc1f807136ebe
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67817
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed