Accellera allows some non-standard values in the second position of the SC_CTHREAD macro. Do that as well, with the same special handling which automatically selects the positive edge of boolean ports/interfaces. Change-Id: I79594980898a17afc30fea6f77384589cbc3c250 Reviewed-on: https://gem5-review.googlesource.com/c/12809 Reviewed-by: Gabe Black <gabeblack@google.com> Maintainer: Gabe Black <gabeblack@google.com>