Add a set of data structures and members analogous to those used for
multiclass defs. These will represent a new kind of multiclass def: a
multidef. The idea behind the multidef is to process a list of items
and create a def record for each one inside the enclosing multiclass.
This allows the user to dynamically create a set of defs based on the
contents of a list.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141230 91177308-0d34-0410-b5e6-96231b3b80d8
