Bug #1450: Illumos should be buildable with GCC4
hat_sfmmu should verify that shared context identifiers are in-bounds
GCC4 notices that we don't check the bounds of the region cookie when unlocking a shared region on SPARC. It is very likely that the (passed-in) cookie will always be valid, and in fact we assert it is so in DEBUG kernels. We may as well VERIFY it, instead, so that the check is in release builds and GCC is happy.