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

fusl/src/math/sincosl.c

+#define _GNU_SOURCE
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+void sincosl(long double x, long double *sin, long double *cos)
+{
+        double sind, cosd;
+        sincos(x, &sind, &cosd);
+        *sin = sind;
+        *cos = cosd;
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+void sincosl(long double x, long double *sin, long double *cos)
+{
+        union ldshape u = {x};
+        unsigned n;
+        long double y[2], s, c;
+
+        u.i.se &= 0x7fff;
+        if (u.i.se == 0x7fff) {
+                *sin = *cos = x - x;
+                return;
+        }
+        if (u.f < M_PI_4) {
+                if (u.i.se < 0x3fff - LDBL_MANT_DIG) {
+                        /* raise underflow if subnormal */
+                        if (u.i.se == 0) FORCE_EVAL(x*0x1p-120f);
+                        *sin = x;
+                        /* raise inexact if x!=0 */
+                        *cos = 1.0 + x;
+                        return;
+                }
+                *sin = __sinl(x, 0, 0);
+                *cos = __cosl(x, 0);
+                return;
+        }
+        n = __rem_pio2l(x, y);
+        s = __sinl(y[0], y[1], 1);
+        c = __cosl(y[0], y[1]);
+        switch (n & 3) {
+        case 0:
+                *sin = s;
+                *cos = c;
+                break;
+        case 1:
+                *sin = c;
+                *cos = -s;
+                break;
+        case 2:
+                *sin = -s;
+                *cos = -c;
+                break;
+        case 3:
+        default:
+                *sin = -c;
+                *cos = s;
+                break;
+        }
+}
+#endif