std::pair cannot be used with gcc 7.4 (ubuntu 18.04)

[mmaurus]

The orogen generation does not work for tasks which use types based on std::pair using gcc7.4.
Error:

cannot find <TYPE> in registry (Typelib::NotFound)
    Typelib[WARN]: /usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../../include/c++/7.4.0/bits/stl_pair.h:208: ignoring /std/pair</std/basic_string</char>,/std/basic_string</char>>, it has private base classes
    Typelib[WARN]: /usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../../include/c++/7.4.0/bits/stl_vector.h:216: ignoring /std/vector</std/pair</std/basic_string</char>,/std/basic_string</char>>,/std/allocator</std/pair</std/basic_string</char>,/std/basic_string</char>>>> as its element type /std/pair</std/basic_string</char>,/std/basic_string</char>> is ignored as well
    Typelib[WARN]: ignoring <TYPE> since its field <TYPENAME> is of the ignored type /std/vector</std/pair</std/basic_string</char>,/std/basic_string</char>>,/std/allocator</std/pair</std/basic_string</char>,/std/basic_string</char>>>>

[doudou]

For a full description of what is allowed, see https://www.rock-robotics.org/rock-and-syskit/components/defining_types.html.

If you feel like implementing support for pairs, it's probably feasible. In fine, it probably "only" needs a special case to ignore std::pair base classes (which are probably zero-size) since Typelib should be capable to parse the first and second public fields. I say probably, as the C++ standard library has really non-obvious implementations of a few things.