Converted to use flex for tokenizing input so we can use an easier to

Converted to use flex for tokenizing input so we can use an easier to
understand recursive descent parser, we can easily handle more syntax
variety, and we can more easily change the configuration items accepted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15732 91177308-0d34-0410-b5e6-96231b3b80d8