Avoid implicit function declarations due to missing prototypes for
internal functions.

diff -ur db-5.3.28.orig/lang/sql/sqlite/src/test_stat.c db-5.3.28/lang/sql/sqlite/src/test_stat.c
--- db-5.3.28.orig/lang/sql/sqlite/src/test_stat.c	2013-09-09 17:35:06.000000000 +0200
+++ db-5.3.28/lang/sql/sqlite/src/test_stat.c	2022-12-10 14:40:10.362683745 +0100
@@ -136,6 +136,13 @@
 #endif
 
 /*
+** Internal functions used by this test.
+*/
+int sqlite3PagerGet(Pager *pPager, Pgno pgno, DbPage **ppPage);
+void *sqlite3PagerGetData(DbPage *pPg);
+void sqlite3PagerUnref(DbPage *pPg);
+
+/*
 ** Connect to or create a statvfs virtual table.
 */
 static int statConnect(