Major change to tblgen: instead of resolving values every time a class is

finished up, only resolve fully when the def is defined.  This allows things
to be changed and all uses to be propagated through.  This implements
TableGen/LazyChange.td and fixes TemplateArgRename.td in the process.

None of the .td files used in LLVM backends are changed at all by this
patch.

llvm-svn: 21344