include/fpu/softfloat: implement float16_set_sign helper

Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>

include/fpu/softfloat.h

@@ -281,6 +281,11 @@ static inline float16 float16_chs(float16 a)
     return make_float16(float16_val(a) ^ 0x8000);
 }
 
+static inline float16 float16_set_sign(float16 a, int sign)
+{
+    return make_float16((float16_val(a) & 0x7fff) | (sign << 15));
+}
+
 /*----------------------------------------------------------------------------
 | The pattern for a default generated half-precision NaN.
 *----------------------------------------------------------------------------*/