tests/fp: Explicitly set inf-zero-nan rule

tests/fp: Explicitly set inf-zero-nan rule

Explicitly set a rule in the softfloat tests for the inf-zero-nan
muladd special case.  In meson.build we put -DTARGET_ARM in fpcflags,
and so we should select here the Arm rule of
float_infzeronan_dnan_if_qnan.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20241202131347.498124-5-peter.maydell@linaro.org