Make use of the flexible-array feature of C99, when available, to try to

pacify -fsanitize=strict-bounds.  This check-in fixes the core. There is
more yet to do in FTS3, RTREE, and in FTS5.

FossilOrigin-Name: 6fd6b32d06bd6a705e5140cd613af823b8183a6f6a9ceeeedfcf5e8b50821d68

src/wal.c

@@ -597,9 +597,13 @@ struct WalIterator {
     u32 *aPgno;                   /* Array of page numbers. */
     int nEntry;                   /* Nr. of entries in aPgno[] and aIndex[] */
     int iZero;                    /* Frame number associated with aPgno[0] */
-  } aSegment[1];                  /* One for every 32KB page in the wal-index */
+  } aSegment[FLEXARRAY];          /* One for every 32KB page in the wal-index */
 };
 
+/* Size (in bytes) of a WalIterator object suitable for N or fewer segments */
+#define SZ_WALITERATOR(N)  \
+     (offsetof(WalIterator,aSegment)*(N)*sizeof(struct WalSegment))
+
 /*
 ** Define the parameters of the hash tables in the wal-index file. There
 ** is a hash-table following every HASHTABLE_NPAGE page numbers in the
@@ -1960,8 +1964,7 @@ static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){
 
   /* Allocate space for the WalIterator object. */
   nSegment = walFramePage(iLast) + 1;
-  nByte = sizeof(WalIterator)
-        + (nSegment-1)*sizeof(struct WalSegment)
+  nByte = SZ_WALITERATOR(nSegment)
         + iLast*sizeof(ht_slot);
   p = (WalIterator *)sqlite3_malloc64(nByte
       + sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)