We should include where specialization happens when we throw a constraint violation error

Suggested by @Chillee 

Here's an example repro: https://gist.github.com/bobrenjc93/bdbd0e16bcccb9280ba9113b5f647138

Which prints out this stack trace: https://gist.github.com/bobrenjc93/a9eb9b7a3ab6659e6238869eb72fedfc

But it doesn't point to the user LOC that actually caused the specialization

cc @chauhang @penguinwu @ezyang