S12Z: s12z-opc.h: Add extern "C" bracketing

opcodes/
	* s12z-opc.h: Add extern "C" bracketing to help
	  users who wish to use this interface in c++ code.

opcodes/ChangeLog

@@ -1,3 +1,8 @@
+2019-04-24  John Darrington  <john@darrington.wattle.id.au>
+
+        * s12z-opc.h: Add extern "C" bracketing to help
+	users who wish to use this interface in c++ code.
+
 2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>
 
 	* arm-dis.c (coprocessor_opcodes): Document new %J and %K format

opcodes/s12z-opc.h

@@ -22,6 +22,11 @@
 
 #include <stdbool.h>
 
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
 /* An abstraction used to read machine code from a source.  */
 struct mem_read_abstraction_base
 {
@@ -262,6 +267,8 @@ struct memory_operand
 int decode_s12z (enum optr *myoperator, short *osize,
 		 int *n_operands, struct operand **operands,
 		 struct mem_read_abstraction_base *);
-
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* S12Z_OPC_H  */