I made an attempt to fix this in r362978, but all it really did was
confine the issue to the $MACHINE_CPUARCH == "riscv" case. The real
problem is that LINKER_FEATURES is not defined here, so bsd.linker.mk
needs to be included.
This error with cleandir only occurs when META_MODE is disabled, which
explains why it was missed by both CI and myself.
Note that this effectively reverts r362978.
Reported by: mjg
Reviewed by: imp, kevans (in IRC)
5e697f5f22