Make list-identifiers deal with deprecation tags by treating the
`MBEDTLS_DEPRECATED` attribute as an identifier. Treat
`MBEDTLS_DEPRECATED` the same as one would `struct` on a function that
returned a `struct` (e.g. `struct something do_action(int param)`)
When doing ABI/API checking, its useful to have a list of all the
identifiers that are defined in the internal header files, as we
do not promise compatibility for them. This option allows for a
simple method of getting them for use with the ABI checking script.
