cc_defs: Add -rdynamic to linkopts for clang compiler by default

[furushchev]

Closes #630

This change adds default linker option -rdynamic to C++ binaries built with ros2_cpp_binary.
It's enabled only with LLVM toolchain (e.g. https://github.com/hermeticbuild/hermetic-llvm )

[mvukov]

Can we do this in a similar way as for clang? See https://github.com/mvukov/rules_ros2/blob/main/.bazelrc#L51-L53 -- we could have another llvm config there.

[furushchev]

Can we do this in a similar way as for clang? See https://github.com/mvukov/rules_ros2/blob/main/.bazelrc#L51-L53 -- we could have another llvm config there.

Hmm, this parameter is only necessary for binaries that link to the pluginlib library, so there's no need to set it globally. Therefore, I think it would be better to configure it in the current PR rather than writing it in .bazelrc.

[mvukov]

This is llvm specific, so, I'd prefer to have this in an llvm config.