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

fusl/src/math/asinhl.c

+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double asinhl(long double x)
+{
+        return asinh(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+/* asinh(x) = sign(x)*log(|x|+sqrt(x*x+1)) ~= x - x^3/6 + o(x^5) */
+long double asinhl(long double x)
+{
+        union ldshape u = {x};
+        unsigned e = u.i.se & 0x7fff;
+        unsigned s = u.i.se >> 15;
+
+        /* |x| */
+        u.i.se = e;
+        x = u.f;
+
+        if (e >= 0x3fff + 32) {
+                /* |x| >= 0x1p32 or inf or nan */
+                x = logl(x) + 0.693147180559945309417232121458176568L;
+        } else if (e >= 0x3fff + 1) {
+                /* |x| >= 2 */
+                x = logl(2*x + 1/(sqrtl(x*x+1)+x));
+        } else if (e >= 0x3fff - 32) {
+                /* |x| >= 0x1p-32 */
+                x = log1pl(x + x*x/(sqrtl(x*x+1)+1));
+        } else {
+                /* |x| < 0x1p-32, raise inexact if x!=0 */
+                FORCE_EVAL(x + 0x1p120f);
+        }
+        return s ? -x : x;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double asinhl(long double x)
+{
+        return asinh(x);
+}
+#endif