os2: return an error code correctly when a child was signaled

For example, a child process terminates due to abort().

    modified:   os2.c

os2.c

@@ -478,6 +478,9 @@ int execve(const char *name, char * const *argv, char * const *envp)
 	/* Is this possible ? And is this right ? */
 	if (rc == -1)
 		return -1;
+
+	if (WIFSIGNALED(status))
+		_exit(ksh_sigmask(WTERMSIG(status)));
 
 	_exit(WEXITSTATUS(status));
 }