Only recreate the incremental OS X MAR files if we need to take OS X signatures into account
In the wake of recreating the .mar files for #19410 (moved) there is no need to do so for non-OS X platforms. But currently this is done.
In the wake of recreating the .mar files for #19410 (moved) there is no need to do so for non-OS X platforms. But currently this is done.