Merge pull request citusdata#52 from citusdata/fix-PG11-build-failure

Fix PostgreSQL 11 build failure

Author: Burak Yücesoy

hll.c

@@ -2756,11 +2756,19 @@ setup_multiset(MemoryContext rcontext)
     MemoryContext oldcontext;
     multiset_t * msp;
 
+#if (PG_VERSION_NUM >= 110000)
+    tmpcontext = AllocSetContextCreateExtended(rcontext,
+                                               "multiset",
+                                               ALLOCSET_DEFAULT_MINSIZE,
+                                               ALLOCSET_DEFAULT_INITSIZE,
+                                               ALLOCSET_DEFAULT_MAXSIZE);
+#else
     tmpcontext = AllocSetContextCreate(rcontext,
                                        "multiset",
                                        ALLOCSET_DEFAULT_MINSIZE,
                                        ALLOCSET_DEFAULT_INITSIZE,
                                        ALLOCSET_DEFAULT_MAXSIZE);
+#endif
 
     oldcontext = MemoryContextSwitchTo(tmpcontext);