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

fusl/src/thread/pthread_condattr_setclock.c

Index: fusl/src/thread/pthread_condattr_setclock.c
diff --git a/fusl/src/thread/pthread_condattr_setclock.c b/fusl/src/thread/pthread_condattr_setclock.c
new file mode 100644
index 0000000000000000000000000000000000000000..71125941341d1392661eccdf6367793d270b0c2a
--- /dev/null
+++ b/fusl/src/thread/pthread_condattr_setclock.c
@@ -0,0 +1,9 @@
+#include "pthread_impl.h"
+
+int pthread_condattr_setclock(pthread_condattr_t *a, clockid_t clk)
+{
+	if (clk < 0 || clk-2U < 2) return EINVAL;
+	a->__attr &= 0x80000000;
+	a->__attr |= clk;
+	return 0;
+}