Remove std::binary_function usage

[aladram]

This pull request removes an inherit of std::binary_function for the struct strcmp_wrapper, a C-style string comparator.

The struct strcmp_wrapper is used by the IDTopicMap typedef (line 276) which is a std::map, and std::map requires strcmp_wrapper to fulfill the Compare named requirement. The inherit of std::binary_function only defines 3 types: first_argument_type, second_argument_type and result_type (typedefs of types passed in argument), which is useless here because they are not part of the requirement.

std::binary_function has been deprecated in C++11, removed in C++17. This change may seem useless, but this change enables us to compile C++17 ROS2 packages using rclcpp (or at least some of them), which may be useful.

[wjwwood]

I wrote this originally, but I don't remember much about it :D, and I was probably following some online recommendation on how to make the strcmp wrapper.

This seems reasonable to me, but we'll have to run CI on it to see if it breaks older compilers/c++ standards or not.

[wjwwood]

Here's CI:

• Linux
• Linux-aarch64
• macOS
• Windows

[aladram]

Running CI on a pull request, this also seems reasonable to me! ;) Thanks for triggering the CI build.

[aladram]

Any news? CI looks fine (a test fails for Linux build, but it started to fail on the previous build, and anyway my change does not affect runtime but compile time).

[wjwwood]

lgtm to me, I agree the test failure is unrelated.