sim/m32c: Add missing include getopt.h in main.c

On buildbot gdb-centos-x86_64 we run into:
...
sim/m32c/main.c: In function ‘main’:
sim/m32c/main.c:143:3: error: implicit declaration of function ‘getopt’ \
  [-Werror=implicit-function-declaration]
   while ((o = getopt (argc, argv, "tc:vdm:C")) != -1)
   ^
cc1: all warnings being treated as errors
make[3]: *** [main.o] Error 1
...

Fix this by adding the missing include of getopt.h.

Build on x86_64-linux.

---
 sim/m32c/main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sim/m32c/main.c b/sim/m32c/main.c
index 958ca27ab2b..4ec30c7c7d0 100644
--- a/sim/m32c/main.c
+++ b/sim/m32c/main.c
@@ -29,6 +29,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <setjmp.h>
 #include <signal.h>
 #include <sys/types.h>
+#include <getopt.h>
 
 #ifdef HAVE_SYS_SOCKET_H
 #ifdef HAVE_NETINET_IN_H