Parser Multidef Support

Parser Multidef Support

Add parser support to recognize multidefs.  No processing on the
multidef is done at this point.  The grammar is:

MultiDef = MULTIDEF ObjectName < Value, Declaration, Value > ObjectBody

The first Value must be resolveable to a list and the second Value
must be resolveable to an integer.  The Declaration is a temporary
value used as an iterator to refer to list items during processing.
It may be passed into the ObjectBody where it will be substituted with
the list value used to instantiate each def.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141232 91177308-0d34-0410-b5e6-96231b3b80d8