[Driver] Simplify OptionData. NFC

Hopefully this makes the option data easier to understand and maintain.

 - Group the member variables.
 - Do the initialization in the header as it's less error prone.
 - Rename the Clean method. It was called only once and was
   re-initializing some but not all (?) members. The only useful thing it
   does is dealing with the local lldbinit file so keep that and make the
   name reflect that.

llvm-svn: 348894