target-arm: Signal Underflow when denormal flushed to zero on output On ARM the architecture mandates that when an output denormal is flushed to zero we must set the FPSCR UFC (underflow) bit, so map softfloat's float_flag_output_denormal accordingly. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>