Add a "fork" of musl as //fusl.

fusl/src/math/nextafterf.c

+#include "libm.h"
+
+float nextafterf(float x, float y)
+{
+        union {float f; uint32_t i;} ux={x}, uy={y};
+        uint32_t ax, ay, e;
+
+        if (isnan(x) || isnan(y))
+                return x + y;
+        if (ux.i == uy.i)
+                return y;
+        ax = ux.i & 0x7fffffff;
+        ay = uy.i & 0x7fffffff;
+        if (ax == 0) {
+                if (ay == 0)
+                        return y;
+                ux.i = (uy.i & 0x80000000) | 1;
+        } else if (ax > ay || ((ux.i ^ uy.i) & 0x80000000))
+                ux.i--;
+        else
+                ux.i++;
+        e = ux.i & 0x7f800000;
+        /* raise overflow if ux.f is infinite and x is finite */
+        if (e == 0x7f800000)
+                FORCE_EVAL(x+x);
+        /* raise underflow if ux.f is subnormal or zero */
+        if (e == 0)
+                FORCE_EVAL(x*x + ux.f*ux.f);
+        return ux.f;
+}