Add support for let expressions around an mdef.  This implements a new part of Regression/TableGen/MultiClass.td.
Add support for let expressions around an mdef.  This implements a new part
of Regression/TableGen/MultiClass.td.


git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@30887 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx