rS355473 vastly improved the readability and cleanliness of these Makefiles. Every single one of them follows the same pattern and duplicates the exact same logic.
Now that we have GENERATED/SRCS, split SRCS up into the two parameters we'll use for ${MAKESYSCALLS} rather than assuming a specific ordering of SRCS and include a common sysent.mk to handle the rest. This makes it less tedious to make sweeping changes.