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

fusl/src/thread/cnd_timedwait.c

Index: fusl/src/thread/cnd_timedwait.c
diff --git a/fusl/src/thread/cnd_timedwait.c b/fusl/src/thread/cnd_timedwait.c
new file mode 100644
index 0000000000000000000000000000000000000000..599767937d0526d23c8bc899ae895fd1eb2703e0
--- /dev/null
+++ b/fusl/src/thread/cnd_timedwait.c
@@ -0,0 +1,15 @@
+#include <threads.h>
+#include <errno.h>
+
+int __pthread_cond_timedwait(cnd_t *restrict, mtx_t *restrict, const struct timespec *restrict);
+
+int cnd_timedwait(cnd_t *restrict c, mtx_t *restrict m, const struct timespec *restrict ts)
+{
+	int ret = __pthread_cond_timedwait(c, m, ts);
+	switch (ret) {
+	/* May also return EINVAL or EPERM. */
+	default:        return thrd_error;
+	case 0:         return thrd_success;
+	case ETIMEDOUT: return thrd_timedout;
+	}
+}