ncurses 6.2 - patch 20201128

ncurses 6.2 - patch 20201128

+ add Smulx to alacritty (Christian Duerr).
+ add rep to PuTTY -TD
+ add putty+keypad -TD
+ add another fflush(stdout) in _nc_flush() to handle time-delays in
  the middle of strings such as flash when the application uses
  low-level calls rather than curses (cf: 20161217).
+ modify configure check for c89/c99 aliases of clang to use its
  -std option instead, because some platforms, in particular macOS,
  do not provide workable c89/c99 aliases.