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

fusl/src/math/tanhl.c

+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double tanhl(long double x)
+{
+        return tanh(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+long double tanhl(long double x)
+{
+        union ldshape u = {x};
+        unsigned ex = u.i.se & 0x7fff;
+        unsigned sign = u.i.se & 0x8000;
+        uint32_t w;
+        long double t;
+
+        /* x = |x| */
+        u.i.se = ex;
+        x = u.f;
+        w = u.i.m >> 32;
+
+        if (ex > 0x3ffe || (ex == 0x3ffe && w > 0x8c9f53d5)) {
+                /* |x| > log(3)/2 ~= 0.5493 or nan */
+                if (ex >= 0x3fff+5) {
+                        /* |x| >= 32 */
+                        t = 1 + 0/(x + 0x1p-120f);
+                } else {
+                        t = expm1l(2*x);
+                        t = 1 - 2/(t+2);
+                }
+        } else if (ex > 0x3ffd || (ex == 0x3ffd && w > 0x82c577d4)) {
+                /* |x| > log(5/3)/2 ~= 0.2554 */
+                t = expm1l(2*x);
+                t = t/(t+2);
+        } else {
+                /* |x| is small */
+                t = expm1l(-2*x);
+                t = -t/(t+2);
+        }
+        return sign ? -t : t;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double tanhl(long double x)
+{
+        return tanh(x);
+}
+#endif