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

fusl/src/math/__fpclassifyl.c

+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+int __fpclassifyl(long double x)
+{
+        return __fpclassify(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+int __fpclassifyl(long double x)
+{
+        union ldshape u = {x};
+        int e = u.i.se & 0x7fff;
+        int msb = u.i.m>>63;
+        if (!e && !msb)
+                return u.i.m ? FP_SUBNORMAL : FP_ZERO;
+        if (!msb)
+                return FP_NAN;
+        if (e == 0x7fff)
+                return u.i.m << 1 ? FP_NAN : FP_INFINITE;
+        return FP_NORMAL;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+int __fpclassifyl(long double x)
+{
+        union ldshape u = {x};
+        int e = u.i.se & 0x7fff;
+        u.i.se = 0;
+        if (!e)
+                return u.i2.lo | u.i2.hi ? FP_SUBNORMAL : FP_ZERO;
+        if (e == 0x7fff)
+                return u.i2.lo | u.i2.hi ? FP_NAN : FP_INFINITE;
+        return FP_NORMAL;
+}
+#endif