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

fusl/src/math/ilogb.c

+#include <limits.h>
+#include "libm.h"
+
+int ilogb(double x)
+{
+        #pragma STDC FENV_ACCESS ON
+        union {double f; uint64_t i;} u = {x};
+        uint64_t i = u.i;
+        int e = i>>52 & 0x7ff;
+
+        if (!e) {
+                i <<= 12;
+                if (i == 0) {
+                        FORCE_EVAL(0/0.0f);
+                        return FP_ILOGB0;
+                }
+                /* subnormal x */
+                for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
+                return e;
+        }
+        if (e == 0x7ff) {
+                FORCE_EVAL(0/0.0f);
+                return i<<12 ? FP_ILOGBNAN : INT_MAX;
+        }
+        return e - 0x3ff;
+}