Results from buildfarm member opossum suggest that this doesn't work
quite right on that platform.  We've seen issues with NaN support on
MIPS/NetBSD before ... allegedly they fixed this stuff back in 2010,
but maybe only for small values of "fixed".

If, in fact, opossum fails this test then I plan to revert it;
it's mainly for diagnostic purposes rather than something we'd
necessarily keep long-term.  I think that the failures in window.sql
could be worked around with some code duplication, but I want to
verify my theory about the cause first.