Separate enum from struct

Otherwise the enum symbols are not visible outside the struct in C++.
Reviewed-by: Thomas Munro <thomas.munro@enterprisedb.com>

src/include/utils/jsonb.h

@@ -219,16 +219,8 @@ typedef struct
 #define JB_ROOT_IS_ARRAY(jbp_)	( *(uint32*) VARDATA(jbp_) & JB_FARRAY)
 
 
-/*
- * JsonbValue:	In-memory representation of Jsonb.  This is a convenient
- * deserialized representation, that can easily support using the "val"
- * union across underlying types during manipulation.  The Jsonb on-disk
- * representation has various alignment considerations.
- */
-struct JsonbValue
+enum jbvType
 {
-	enum
-	{
 	/* Scalar types */
 	jbvNull = 0x0,
 	jbvString,
@@ -239,7 +231,17 @@ struct JsonbValue
 	jbvObject,
 	/* Binary (i.e. struct Jsonb) jbvArray/jbvObject */
 	jbvBinary
-	}			type;			/* Influences sort order */
+};
+
+/*
+ * JsonbValue:	In-memory representation of Jsonb.  This is a convenient
+ * deserialized representation, that can easily support using the "val"
+ * union across underlying types during manipulation.  The Jsonb on-disk
+ * representation has various alignment considerations.
+ */
+struct JsonbValue
+{
+	jbvType		type;			/* Influences sort order */
 
 	union
 	{