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

fusl/src/math/coshl.c

+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double coshl(long double x)
+{
+        return cosh(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+long double coshl(long double x)
+{
+        union ldshape u = {x};
+        unsigned ex = u.i.se & 0x7fff;
+        uint32_t w;
+        long double t;
+
+        /* |x| */
+        u.i.se = ex;
+        x = u.f;
+        w = u.i.m >> 32;
+
+        /* |x| < log(2) */
+        if (ex < 0x3fff-1 || (ex == 0x3fff-1 && w < 0xb17217f7)) {
+                if (ex < 0x3fff-32) {
+                        FORCE_EVAL(x + 0x1p120f);
+                        return 1;
+                }
+                t = expm1l(x);
+                return 1 + t*t/(2*(1+t));
+        }
+
+        /* |x| < log(LDBL_MAX) */
+        if (ex < 0x3fff+13 || (ex == 0x3fff+13 && w < 0xb17217f7)) {
+                t = expl(x);
+                return 0.5*(t + 1/t);
+        }
+
+        /* |x| > log(LDBL_MAX) or nan */
+        t = expl(0.5*x);
+        return 0.5*t*t;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double coshl(long double x)
+{
+        return cosh(x);
+}
+#endif