Duplicate Errors on assignment of *T expression to ptr<T> variable

[lenary]

When converting some benchmarks, I got the following duplicated error messages, in every place where I was assigning something of type *T into a ptr<T> typed variable.

In this particular case, localnode->from_values[i] has type *double and other_value has type ptr<double>

/Users/ashe2/Code/checkedc-llvm-test-suite/MultiSource/Benchmarks/Olden/em3d/em3d.c:27:21: error: expression has no
      bounds, right-hand side of assignment expected to have bounds because the left-hand side has bounds
      other_value = localnode->from_values[i];
                    ^~~~~~~~~~~~~~~~~~~~~~~~~
/Users/ashe2/Code/checkedc-llvm-test-suite/MultiSource/Benchmarks/Olden/em3d/em3d.c:27:21: error: expression has no
      bounds, cast to ptr<T> expects source to have bounds
      other_value = localnode->from_values[i];
                    ^~~~~~~~~~~~~~~~~~~~~~~~~

We should definitely only be emitting one of these errors, not both. I think perhaps the second one is closer to the "truth" (or a truth that reveals the fix), but we should probably be aiming for something like "expression of type *T cannot be cast to ptr<T> implicitly". I'm not sure even mentioning bounds here is useful, as ptr<T>s don't have the same notion of bounds that array_ptr<T> has.

[lenary]

Follow-up:

Attempting an explicit cast shows how these errors are slightly different. I maintain having both is not useful, and I think an explicit cast should get rid of both. My understanding is that explicit casts would not be checked except if you used the special new casts we were introducing.

/Users/ashe2/Code/checkedc-llvm-test-suite/MultiSource/Benchmarks/Olden/em3d/em3d.c:27:21: error: expression has no
      bounds, right-hand side of assignment expected to have bounds because the left-hand side has bounds
      other_value = (_Ptr<double>)localnode->from_values[i];
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/ashe2/Code/checkedc-llvm-test-suite/MultiSource/Benchmarks/Olden/em3d/em3d.c:27:35: error: expression has no
      bounds, cast to ptr<T> expects source to have bounds
      other_value = (_Ptr<double>)localnode->from_values[i];
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~

[dtarditi]

This is fixed.