[Bug target/127872] storing a signaling NaN constant uses flds/fstps and quietens it with -mfpmath=387

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127872

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Similarly

void
copy (float *d, const float *s)
{
  *d = *s;
}

quitens sNaNs.  I suppose generally this could be accepted target behavior
that's not conforming, but given the actual behavior is a bit erratical
and dependent on optimization level this is still a QoI issue.