Make the win32/makefile.mk a little safer

Make the win32/makefile.mk a little safer

- Add a few missing s,\,$B, substitutions. We were living dangerously
  with various unescaped backslashes not causing problems purely because
  they don't make valid ecape codes anyway, e.g. ..\perl59.dll was only
  working because \p isn't an escape code so it didn't get mapped to
  anything nasty.

- Move the $(BLINK_FLAGS) out of $(mktmp ...)'s because it could contain
  backslashes which would otherwise need escaping. (Adding in the
  escaping would be another fix but other cases don't put $(BLINK_FLAGS)
  into $(mktmp ...) files in the first place.)

p4raw-id: //depot/perl@29396