* Don't print out HOW we are running Flex unless in verbose mode. We already

* Don't print out HOW we are running Flex unless in verbose mode.  We already
  hide the bison command line.
* If running flex or bison gives us the files we already have, don't overwrite
  the ones we have, which cause unnecessary compilation.  I demand the ability
  to make meaningless changes without penalty!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7571 91177308-0d34-0410-b5e6-96231b3b80d8