twister: custom simulator needs an exec defined

custom simulator needs an executable defined, or else we will have tests
marked runnable with nothing to run them which would result in an
error/warning.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

scripts/pylib/twister/twisterlib/testinstance.py

@@ -277,7 +277,7 @@ def check_runnable(self,
         if self.testsuite.harness == 'pytest':
             target_ready = bool(filter == 'runnable' or self.platform.simulation in SUPPORTED_SIMS_IN_PYTEST)
 
-        SUPPORTED_SIMS_WITH_EXEC = ['nsim', 'mdb-nsim', 'renode', 'tsim', 'native', 'simics']
+        SUPPORTED_SIMS_WITH_EXEC = ['nsim', 'mdb-nsim', 'renode', 'tsim', 'native', 'simics', 'custom']
         if filter != 'runnable' and \
                 self.platform.simulation in SUPPORTED_SIMS_WITH_EXEC and \
                 self.platform.simulation_exec: