Add a stub implementation of sqlite3Preload when building with system sqlite.

third_party/sqlite/sqlite3.h

Index: third_party/sqlite/sqlite3.h
diff --git a/third_party/sqlite/sqlite3.h b/third_party/sqlite/sqlite3.h
index 8e5618fcf415adae18b455a8c13359ad6d0a9b49..6c7c3b084353456d2dedfa9964e975bed5f637dd 100644
--- a/third_party/sqlite/sqlite3.h
+++ b/third_party/sqlite/sqlite3.h
@@ -11,6 +11,10 @@
 
 #if defined(USE_SYSTEM_SQLITE)
 #include <sqlite3.h>
+
+// A no-op implementation of database preloading (not available
+// when using system sqlite).
+int sqlite3Preload(sqlite3 *db) { return SQLITE_OK; }
 #else
 #include "third_party/sqlite/src/preprocessed/sqlite3.h"
 #endif