Now that all of the necessary bits for ARMv6 support for CloudABI have
been checked in, let's hook the kernel module up to the build and
document its existence.
When fixing this module to build on PC98, I actually broke the build on
ARM64. On PC98 we need to pull in the sources from the MACHINE_CPUARCH
(i386), but on ARM64 we need to use the MACHINE, as MACHINE_CPUARCH is
set to aarch64 instead of just arm64.
Where the cloudabi64 kernel can be used to execute 64-bit CloudABI
binaries, this one should be used for 32-bit binaries. Right now it
works on i386 and amd64.
