Add header guards

src/ops.h

@@ -18,6 +18,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#ifndef _FCEU_OPS_H
+#define _FCEU_OPS_H
+
 case 0x00:  /* BRK */
 			_PC++;
 			PUSH(_PC>>8);
@@ -483,3 +486,5 @@ case 0xFC: LD_ABX(;);
 /* XAA - BIG QUESTION MARK HERE */
 case 0x8B: _A|=0xEE; _A&=_X; LD_IM(AND);
 //endif
+//
+#endif