Really fix cleandir after r362973

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)