ignore-value: make ignore_value more generic; deprecate ignore_ptr

ignore-value: make ignore_value more generic; deprecate ignore_ptr

* lib/ignore-value.h: Include <stdint.h>, for decl of intptr_t.
(ATTRIBUTE_DEPRECATED): Define.
(_ignore_case): New function.
(ignore_value): New macro, to replace the old function.
(ignore_ptr): Arrange for any use to evoke a deprecation warning.
* modules/ignore-value (Depends-on): Add stdint.