test/common: add tests for endianness and single bit signs in floats
test/common: add tests for endianness and single bit signs in floats

If these fail anywhere we can probably deal with that, but I don't
think SIMDe is likely to run on such targets.  If any of these fail
on your target please get in touch and we can try to figure something
out.

nemequ/simde,nemequ/simde,nemequ/simde