Merge pull request #68 from erikmata/fix-missing-VARDATA-symbol

Fixes missing VARDATA symbol in PG16
diff --git a/src/common.c b/src/common.c
index f9a11f1..9e8ef34 100644
--- a/src/common.c
+++ b/src/common.c
@@ -22,6 +22,12 @@
 
 #include "base64.h"
 
+// Since version 16 of PG, all functionality for variable-length
+// data was moved from postgres.h into the new file varatt.h
+#if PG_VERSION_NUM >= 160000
+#include "varatt.h"
+#endif
+
 PG_MODULE_MAGIC;
 
 PG_FUNCTION_INFO_V1(pg_sketch_in);