Add an optimization that attempts to run a subquery as a coroutine rather

than manifesting it into a temporary table.

FossilOrigin-Name: 7af3acbbd49a2114fcdada9ec907c68ba9b053bd

src/delete.c

@@ -112,6 +112,7 @@ void sqlite3MaterializeView(
       sqlite3SelectDelete(db, pDup);
     }
     pDup = sqlite3SelectNew(pParse, 0, pFrom, pWhere, 0, 0, 0, 0, 0, 0);
+    if( pDup ) pDup->selFlags |= SF_Materialize;
   }
   sqlite3SelectDestInit(&dest, SRT_EphemTab, iCur);
   sqlite3Select(pParse, pDup, &dest);