Use hermetic ckati/makeparallel prebuilts

Currently, we're building against the native host version of libc++ and
other headers. Instead, use prebuilts of ckati/makeparallel built with
Soong against the included libc++ and sysroot. Building ckati /
makeparallel doesn't work well in unbundled branches that don't have all
of the libc++ dependencies to do successful host builds.

KATI is default variable defined when running under Kati, don't use it
for other purposes. Use CKATI instead.

Bug: 27533820
Change-Id: I82d66f5e34e3341a3cee4c5c83cd1d9a54d057ff