Fix FMULX not squashing denormalized inputs when FZ is set.

Fix FMULX not squashing denormalized inputs when FZ is set.

While FMULX returns a 2.0f float when two operators are infinity and
zero, those operators should be unpacked from raw inputs first. Inconsistent
cases would occur when operators are denormalized floats in flush-to-zero
mode. A wrong codepath will be entered and 2.0f will not be returned
without this patch.
Fix by checking whether inputs need to be flushed before running into
different codepaths.

Signed-off-by: Xiangyu Hu <[email protected]>
Message-id: 1422459650[email protected]
Signed-off-by: Peter Maydell <[email protected]>