TableGen: Location information for diagnostic.

TableGen: Location information for diagnostic.

def Pat<...>;

Results in 'record name is not a string!' diagnostic. Not the best,
but the lack of location information moves it from not very helpful
into completely useless. We're in the Record class when throwing the
error, so just add the location info directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160098 91177308-0d34-0410-b5e6-96231b3b80d8