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

fusl/src/math/tanl.c

+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double tanl(long double x)
+{
+        return tan(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+long double tanl(long double x)
+{
+        union ldshape u = {x};
+        long double y[2];
+        unsigned n;
+
+        u.i.se &= 0x7fff;
+        if (u.i.se == 0x7fff)
+                return x - x;
+        if (u.f < M_PI_4) {
+                if (u.i.se < 0x3fff - LDBL_MANT_DIG/2) {
+                        /* raise inexact if x!=0 and underflow if subnormal */
+                        FORCE_EVAL(u.i.se == 0 ? x*0x1p-120f : x+0x1p120f);
+                        return x;
+                }
+                return __tanl(x, 0, 0);
+        }
+        n = __rem_pio2l(x, y);
+        return __tanl(y[0], y[1], n&1);
+}
+#endif