Add logic to releasetest.tcl that detects -fsanitize=undefined errors.

Fix a few false-positivies that come up when running the sanitize=undefined
test.

FossilOrigin-Name: 2835e79a0afec6e4d449ac9340afec068c2d4c11

src/test8.c

@@ -648,12 +648,12 @@ static int echoRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
 ** indeed the hash of the supplied idxStr.
 */
 static int hashString(const char *zString){
-  int val = 0;
+  u32 val = 0;
   int ii;
   for(ii=0; zString[ii]; ii++){
     val = (val << 3) + (int)zString[ii];
   }
-  return val;
+  return (int)(val&0x7fffffff);
 }
 
 /*