Description

See: https://build.ros2.org/job/Jdev__gtsam__ubuntu_noble_amd64/136/

Why?

Reason: the use of embedded Eigen version by default leads to not using the SYSTEM flag for those includes, so any warning there is treated as an error.

Solutions

To modify CMake scripts so..

1. Use Eigen from the system version by default,
2. Like (1), but only when it's detected we are building for the ROS build farm (kida hack, but have been there...)
3. Add the SYSTEM flag to embedded version of Eigen (if not done already, right? @Gold856 )

What do you think, @dellaert ?

I would like (1), but I know you like backwards compatible behavior, so the second choice would probably be (3), and if it's already done but is not working for some cmake limitation (cannot use SYSTEM for non-system directories? never checked that..), then use (2).