Perhaps better to drop the SSE2 bits completely.  Anybody who
actually wants SSE2 instructions in their binary can do a

CC="gcc -msse2 -mfpmath=sse" configure && ...

Unless there are objections, I'll drop everything involving SSE2 from 
the configure script.

It's a bit of a shame, though:  it's definitely desirable to be using 
the SSE2 instructions for floating-point whenever possible.  Fewer 
surprises due to double rounding or random 80-bit register spilling, 
better performance on underflow and NaNs, ...