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

fusl/src/time/timer_getoverrun.c

Index: fusl/src/time/timer_getoverrun.c
diff --git a/fusl/src/time/timer_getoverrun.c b/fusl/src/time/timer_getoverrun.c
new file mode 100644
index 0000000000000000000000000000000000000000..e7f891e4040fe3ff3117a15dec1bbab70cc75ad1
--- /dev/null
+++ b/fusl/src/time/timer_getoverrun.c
@@ -0,0 +1,12 @@
+#include <time.h>
+#include <limits.h>
+#include "pthread_impl.h"
+
+int timer_getoverrun(timer_t t)
+{
+	if ((intptr_t)t < 0) {
+		pthread_t td = (void *)((uintptr_t)t << 1);
+		t = (void *)(uintptr_t)(td->timer_id & INT_MAX);
+	}
+	return syscall(SYS_timer_getoverrun, t);
+}