Final patch.
Skip, could you please give this one a try, and then with any luck this
can be fixed for 3.0.1. (Sorry for creating more work; this should be
the last time.)
I've added a configure test that detects x87 FPU usage, via the double
rounding issue associated with the x87. If x87 is detected then
_Py_force_double is used via a macro Py_FORCE_DOUBLE; otherwise,
Py_FORCE_DOUBLE does nothing.
When you configure on a machine that uses x87, you should see:
checking for x87-style double rounding... yes
in the configure output.