Fix compatibility with pg18 (#70)

Upstream commit postgres/postgres@525392d changed return type of
ExecutorStart_hook API from void to bool.

Author: RekGRpth

pg_qualstats.c

@@ -109,6 +109,14 @@ PG_MODULE_MAGIC;
 #define ParallelLeaderBackendId ParallelMasterBackendId
 #endif
 
+/* ExecutorStart hook */
+#if PG_VERSION_NUM >= 180000
+#define EXEC_START_RET	bool
+#else
+#define EXEC_START_RET	void
+#endif
+/* end of ExecutorStart hook */
+
 /*
  * Extension version number, for supporting older extension versions' objects
  */
@@ -145,7 +153,7 @@ static void pgqs_backend_mode_startup(void);
 static void pgqs_shmem_request(void);
 #endif
 static void pgqs_shmem_startup(void);
-static void pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags);
+static EXEC_START_RET pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags);
 static void pgqs_ExecutorRun(QueryDesc *queryDesc,
 				 ScanDirection direction,
 #if PG_VERSION_NUM >= 90600
@@ -604,7 +612,7 @@ pgqs_fillnames(pgqsEntryWithNames *entry)
 /*
  * Request rows and buffers instrumentation if pgqs is enabled
  */
-static void
+static EXEC_START_RET
 pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags)
 {
 	/* Setup instrumentation */
@@ -636,9 +644,9 @@ pgqs_ExecutorStart(QueryDesc *queryDesc, int eflags)
 			queryDesc->instrument_options |= PGQS_FLAGS;
 	}
 	if (prev_ExecutorStart)
-		prev_ExecutorStart(queryDesc, eflags);
+		return prev_ExecutorStart(queryDesc, eflags);
 	else
-		standard_ExecutorStart(queryDesc, eflags);
+		return standard_ExecutorStart(queryDesc, eflags);
 
 }