getopt: fix null pointer arithmetic ub

[musl] / src / math / copysignf.c

#include <math.h>
#include <stdint.h>

float copysignf(float x, float y)
{
        union {float f; uint32_t i;} ux={x}, uy={y};
        ux.i &= 0x7fffffff;
        ux.i |= uy.i & 0x80000000;
        return ux.f;
}