Allow building with debug

[henriksod]

I have had to run some debugging in the investigation of this issue ros2/rmw_fastrtps#703. To do that I had to do some changes like adding a debug flag to control Cmake properties like CMAKE_BUILD_TYPE.

I think this could be useful to add support for. In essence, what is needed is to adapt the Cmake built libraries with a custom flag since I am not sure there is another way to control that via the build command.

See this example:
https://github.com/henriksod/rules_ros2/blob/feature/debug

Adds bazel build ... --config=debug.

Then I run gdb on the produced binaries like:
AMENT_PREFIX_PATH="generic_publisher_tests_launch_ament_setup" gdb generic_publisher_tests_impl

[henriksod]

I actually just noticed this line in foreign rules cc https://github.com/bazelbuild/rules_foreign_cc/blob/816905a078773405803e86635def78b61d2f782d/foreign_cc/cmake.bzl#L208

Seems like we should not force set CMAKE_BUILD_TYPE after all.

Use bazel build ... --compilation_mode=dbg to set global debug mode. Release mode is default.

[mvukov]

If you have a bit of time, please open a PR and clean up CMAKE_BUILD_TYPE occurrences.

[mvukov]

BTW, if you want to run a target under gdb, do: bazel run --run_under="gdb" //path/to:target.

[henriksod]

Yeah I had some issues with that when running the nodes with this argument, will try to use this again :-)