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

fusl/src/time/clock_gettime.c

+#include <time.h>
+#include <errno.h>
+#include <stdint.h>
+#include "syscall.h"
+#include "libc.h"
+#include "atomic.h"
+
+static int sc_clock_gettime(clockid_t clk, struct timespec *ts)
+{
+        int r = __syscall(SYS_clock_gettime, clk, ts);
+        if (!r) return r;
+        if (r == -ENOSYS) {
+                if (clk == CLOCK_REALTIME) {
+                        __syscall(SYS_gettimeofday, ts, 0);
+                        ts->tv_nsec = (int)ts->tv_nsec * 1000;
+                        return 0;
+                }
+                r = -EINVAL;
+        }
+        errno = -r;
+        return -1;
+}
+
+void *__vdsosym(const char *, const char *);
+
+int __clock_gettime(clockid_t clk, struct timespec *ts)
+{
+#ifdef VDSO_CGT_SYM
+        static int (*volatile cgt)(clockid_t, struct timespec *);
+        if (!cgt) {
+                void *f = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
+                if (!f) f = (void *)sc_clock_gettime;
+                a_cas_p(&cgt, 0, f);
+        }
+        return cgt(clk, ts);
+#else
+        return sc_clock_gettime(clk, ts);
+#endif
+}
+
+weak_alias(__clock_gettime, clock_gettime);