Thanks.  uname looks like the way to go, then.

Is your copy of OpenSolaris running in 32-bit mode or 64-bit mode?  Does
the mode make a difference to the output of uname, or is uname -p always
i386, regardless of the mode?

I think the configure test for the inline assembly should go ahead on
both x86 and x86-64:  it seems likely that a 64-bit OS would be using
SSE2 instructions for floating-point (which would make setting and
getting the x87 control word unnecessary) instead of the x87 FPU, but I
don't know that for sure.

Actually, I guess I could just make that configure test unconditional.
It'll fail on non-x86 hardware, but that's no big deal.