TF causing casting compiler warnings in strict mode

[davetcoleman]

Adding to my random ROS package's CMake:

add_definitions(-W -Wall -Wextra
  -Wcast-qual -Wwrite-strings -Wunreachable-code -Wpointer-arith
  -Winit-self -Wredundant-decls
  -Wno-unused-parameter -Wno-unused-function)

TF starts having lots of warnings, e.g. in /opt/ros/jade/include/tf/LinearMath/Vector3.h

/opt/ros/jade/include/tf/LinearMath/Vector3.h:626:42: warning: cast from type ‘const tfScalar* {aka const double*}’ to type ‘unsigned char*’ casts away qualifiers [-Wcast-qual]
  unsigned char* src  = (unsigned char*) &sourceVal;
                                          ^
In file included from /opt/ros/jade/include/tf2/transform_storage.h:35:0,
                 from /opt/ros/jade/include/tf2/buffer_core.h:35,
                 from /opt/ros/jade/include/tf2_ros/buffer_interface.h:35,
                 from /opt/ros/jade/include/tf2_ros/buffer.h:35,
                 from /opt/ros/jade/include/tf/tf.h:48,

[tfoote]

This is doing byte ordering swapping for endianness. Its a valid warning in general but in this case it's actually correct. If you'd like to submit a PR to suppress the warnings that would be considered.

https://github.com/ros/geometry/blob/indigo-devel/tf/include/tf/LinearMath/Vector3.h#L626

Though this is a fork of the bullet linear math library and it would be better to submit the patch upstream and we can port back the changes.

https://github.com/bulletphysics/bullet3/blob/master/src/LinearMath/btVector3.h#L1231

We've had trouble in the past due to diverging from upstream when we applied patches locally that weren't accepted upstream.