This will modify the default behavior to select BUILD_IDLC based on
whether Maven is discovered or not.
The behavior when `-DBUILD_IDLC` is specified on the command line remains
unchanged - the build will maintain the current behavior of failing to
configure if `BUILD_IDLC=ON` and Maven was later not found.
This reverts (part of) commit 860a6aadae.
Signed-off-by: Scott K Logan <logans@cottsay.net>
This will eliminate two large dependencies when building CycloneDDS with
colcon for ROS 2, which doesn't appear to need the IDLC.
Signed-off-by: Scott K Logan <logans@cottsay.net>
