Simplify llvm::cl::Option by using a bit field instead of manual bit packing.

This still preserves the same total layout.

Previously it looked like:
*** Dumping AST Record Layout
   0 | class llvm::cl::Option
   0 |   (Option vtable pointer)
   8 |   int NumOccurrences
  12 |   int Flags
  16 |   unsigned int Position
  20 |   unsigned int AdditionalVals
  24 |   class llvm::cl::Option * NextRegistered
  32 |   const char * ArgStr
  40 |   const char * HelpStr
  48 |   const char * ValueStr
  sizeof=56, dsize=56, align=8
  nvsize=56, nvalign=8

Now it looks like:
*** Dumping AST Record Layout
   0 | class llvm::cl::Option
   0 |   (Option vtable pointer)
   8 |   int NumOccurrences
  12 |   enum NumOccurrencesFlag Occurrences
  12 |   unsigned int Value
  12 |   enum OptionHidden HiddenFlag
  12 |   enum FormattingFlags Formatting
  13 |   unsigned int Misc
  16 |   unsigned int Position
  20 |   unsigned int AdditionalVals
  24 |   class llvm::cl::Option * NextRegistered
  32 |   const char * ArgStr
  40 |   const char * HelpStr
  48 |   const char * ValueStr
  sizeof=56, dsize=56, align=8
  nvsize=56, nvalign=8

llvm-svn: 148736