tcg/tcg-op.h: Add multiple include guard

The tcg-op.h header was missing the usual guard against multiple
inclusion; add it.

(Spotted by lgtm.com's static analyzer.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181108125256.30986-1-peter.maydell@linaro.org

tcg/tcg-op.h

@@ -22,6 +22,9 @@
  * THE SOFTWARE.
  */
 
+#ifndef TCG_TCG_OP_H
+#define TCG_TCG_OP_H
+
 #include "tcg.h"
 #include "exec/helper-proto.h"
 #include "exec/helper-gen.h"
@@ -1267,3 +1270,5 @@ static inline void tcg_gen_trunc_ptr_i32(TCGv_i32 r, TCGv_ptr a)
 
 #undef PTR
 #undef NAT
+
+#endif /* TCG_TCG_OP_H */