hcrypto: Avoid arc4random in kernel

hcrypto: Avoid arc4random in kernel

Our HAVE_ARC4RANDOM symbol represents the availability of arc4random()
in userspace, not in the kernel. On Solaris, we'll define
HAVE_ARC4RANDOM, but the built kernel module will be unusable, since
we cannot resolve the arc4random symbol.

To to avoid this, undef HAVE_ARC4RANDOM when building hcrypto for the
kernel, just like we do with HAVE_GETUID.

Reviewed-on: https://gerrit.openafs.org/12946
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 6082243e42525c738239fe429bcb64e0e4f22207)

Change-Id: I41c4c6f65581aee3d53a7c4b8f6c108f88631e3f
Reviewed-on: https://gerrit.openafs.org/13101
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>