Use different capsule names with and without -builtin

[eltoder]

Types generated with and without -builtin are not compatible. Mixing
them in a common type list leads to crashes. Avoid this by using
different capsule names: "type_pointer_capsule" without -builtin and
"type_pointer_capsule_builtin" with.

See #1684

[wsfulton]

Thanks for the patch @eltoder. Kudos for squeezing this into the test-suite and forcing/overriding when -builtin is used! I would have said the test framework was not designed for this type of flexibility. Although clever, the implementation for the test is not what I'd call particularly maintainable nor easy to follow, which I think is important, so I've put in an alternative, which is not ideal either, but I feel is at least more maintainable. See f2dd436 which enabled another improvement in c5f2097.

[eltoder]

Thank you for merging @wsfulton. Yes, the test suite did not cooperate, but it felt bad to fix something very subtle without any tests. I did not want to spend a lot of time refactoring, since I wasn't sure if there was any interest in merging. I considered an approach similar to f2dd436. My approach seemed more general and not too messy, until I realized that I'm limited to sh syntax and cannot use bash's indirect variables. I'm fine with either option. Thank you for polishing the test, hopefully this will not regress in the future.