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

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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21344 91177308-0d34-0410-b5e6-96231b3b80d8