TblGen diagnostic for mismatched template instantiation.

Providing a template argment to a non-templatized class was crashing
tblgen. Add a diagnostic.

For example,
$ cat bug.td
class A;

def B : A<0> {
}
$ llvm-tblgen bug.td
bug.td:3:11: error: template argument provided to non-template class
def B : A<0> {
          ^

llvm-svn: 148565