Hexagon (target/hexagon) properly handle NaN in dfmin/dfmax/sfmin/sfmax

The float??_minnum implementation differs from Hexagon for SNaN,
it returns NaN, but Hexagon returns the other input.  So, we use
float??_minimum_number.

Test cases added to tests/tcg/hexagon/fpstuff.c

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20220308190410.22355-1-tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>