message: Get XlaCompile attr errors out of all of our gradient stack traces
  Python helpfully appends the error from the "try" portion to new errors from calling grad_fn in "except", but it's 100% irrelevant in this case.
diff: @@ -333,7 +333,7 @@ def _MaybeCompile(scope, op, func, grad_fn):
  "_XlaSeparateCompiledGradients")
  xla_scope = op.get_attr("_XlaScope").decode()
  except ValueError:
  - return grad_fn() # Exit early
  + xla_compile = False
  if not xla_compile:
  return grad_fn() # Exit early
  