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

fusl/src/signal/sigtimedwait.c

Index: fusl/src/signal/sigtimedwait.c
diff --git a/fusl/src/signal/sigtimedwait.c b/fusl/src/signal/sigtimedwait.c
new file mode 100644
index 0000000000000000000000000000000000000000..0739986b1959b9919c86974dcc7babee79877d2a
--- /dev/null
+++ b/fusl/src/signal/sigtimedwait.c
@@ -0,0 +1,13 @@
+#include <signal.h>
+#include <errno.h>
+#include "syscall.h"
+#include "libc.h"
+
+int sigtimedwait(const sigset_t *restrict mask, siginfo_t *restrict si, const struct timespec *restrict timeout)
+{
+	int ret;
+	do ret = syscall_cp(SYS_rt_sigtimedwait, mask,
+		si, timeout, _NSIG/8);
+	while (ret<0 && errno==EINTR);
+	return ret;
+}