target/xtensa: Explicitly set 2-NaN propagation rule

target/xtensa: Explicitly set 2-NaN propagation rule

Set the NaN propagation rule explicitly in xtensa_use_first_nan().

(When we convert the softfloat pickNaNMulAdd routine to also
select a NaN propagation rule at runtime, we will be able to
remove the use_first_nan flag because the propagation rules
will handle everything.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241025141254.2141506-15-peter.maydell@linaro.org