Oh, wait. I just stumbled upon arch/i386/kernel/cpu/intel_cacheinfo.c
that references the callback function from generic CPU-initialization
startup code that must get executed even when HOTPLUG_CPU=n. The leave-it-
upto-toolchain method would see this reference, and preserve the function
even after initcalls stage for HOTPLUG_CPU=n. So the explicit __cpuinit
method scores here, admittedly only because of weird taste of said code.
-