sim: cris: add unistd.h for environ decl

We include environ.h for the fallback, but we still need to include
unistd.h in case it provides it as gnulib will detect.

sim/cris/ChangeLog

@@ -1,3 +1,7 @@
+2021-05-23  Mike Frysinger  <vapier@gentoo.org>
+
+	* sim-if.c: Include unistd.h.
+
 2021-05-17  Mike Frysinger  <vapier@gentoo.org>
 
 	* sim-main.h (struct sim_state): Delete.

sim/cris/sim-if.c

@@ -30,6 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "sim-main.h"
 #include <stdlib.h>
 #include <errno.h>
+#include <unistd.h>
 #include "sim-options.h"
 #include "dis-asm.h"
 #include "environ.h"