Fix #34172: cycles BVH build crashing in some rare circumstances on 32 bit linux.

The problem was (again) the x86 extended precision float register being used for
one float value while the other was rounded to lower precision. This caused the
strictly weak order requirement for std::sort to be broken.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56303 954f8c5b-7b00-dc11-b283-0030488c597c