Use modern CMake method to add compile options

[RoboticsYY]

This PR intends to use modern CMake method add_compile_options to add compile options and to align with ROS2 standard. Still use set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-redundant-decls"), because add_compile_options will not reach the targets generated from the rosidl.

[rhaschke]

I don't see why add_compile_options doesn't affect rosidl. The link doesn't provide an explanation.

[RoboticsYY]

I don't see why add_compile_options doesn't affect rosidl. The link doesn't provide an explanation.

My understanding is that add_compile_options only appends COMPILE_OPTIONS to the targets created by the followed add_library() or add_executable(). However, setting CMAKE_CXX_FLAGS can change the variables in the cmake cache file of the package's build directory. And this can affects the files in the build directory generated by rosidl.

For the redundant declarations of rosidl, I have filed up a issue here.