Fix an instance of signed arithmetic overflow and an one bit-shift overflow.

Mark six other signed arithmetic overflow locations that need fixing.

FossilOrigin-Name: 04abab71ecd52f6070b9f84781a3df3d6dba7722

src/printf.c

@@ -400,7 +400,7 @@ void sqlite3VXPrintf(
             v = va_arg(ap,int);
           }
           if( v<0 ){
-            longvalue = -v;
+            longvalue = -v;  /* CLANG */
             prefix = '-';
           }else{
             longvalue = v;