tests/fp: Explicitly set 2-NaN propagation rule

tests/fp: Explicitly set 2-NaN propagation rule

Explicitly set a 2-NaN propagation rule in the softfloat tests.  In
meson.build we put -DTARGET_ARM in fpcflags, and so we should select
here the Arm propagation rule of float_2nan_prop_s_ab.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241025141254.2141506-3-peter.maydell@linaro.org