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

fusl/src/thread/__syscall_cp.c

+#include "pthread_impl.h"
+#include "syscall.h"
+
+__attribute__((__visibility__("hidden")))
+long __syscall_cp_c();
+
+static long sccp(syscall_arg_t nr,
+                 syscall_arg_t u, syscall_arg_t v, syscall_arg_t w,
+                 syscall_arg_t x, syscall_arg_t y, syscall_arg_t z)
+{
+        return (__syscall)(nr, u, v, w, x, y, z);
+}
+
+weak_alias(sccp, __syscall_cp_c);
+
+long (__syscall_cp)(syscall_arg_t nr,
+                    syscall_arg_t u, syscall_arg_t v, syscall_arg_t w,
+                    syscall_arg_t x, syscall_arg_t y, syscall_arg_t z)
+{
+        return __syscall_cp_c(nr, u, v, w, x, y, z);
+}