target/sh4: fix FPU unorderered compare

In case of unordered compare, the fcmp instructions should either
trigger and invalid exception (if enabled) or set T=0. The existing code
left it unchanged.

LP: https://bugs.launchpad.net/qemu/+bug/1701821
Reported-by: Bruno Haible <bruno@clisp.org>
Message-Id: <20170702202814.27793-3-aurelien@aurel32.net>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
