1.0.42.18: let's take that again

 Previous commit was supposed to have this commit message:

 "OpenBSD build fix -- signal handlers need to lead FPU control word"

 * Patch by Josh Elsasser, lp#615492.

   In his words:

   OpenBSD/amd64 recently began running signal handlers with a clean
   FPU state, making it necessary to load the floating point control
   word. The attached patch does exactly this, and works equally well
   on OpenBSD systems from both before and after the signal handler
   change was made.

   This patch is necessary to build SBCL x86-64 on recent -current
   snapshots of OpenBSD, and for the upcoming 4.8 release.

 * Committing untested, as I don't have OpenBSD handy.