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

fusl/src/thread/pthread_barrier_destroy.c

Index: fusl/src/thread/pthread_barrier_destroy.c
diff --git a/fusl/src/thread/pthread_barrier_destroy.c b/fusl/src/thread/pthread_barrier_destroy.c
new file mode 100644
index 0000000000000000000000000000000000000000..4ce0b2e1278499de5e417f870d4e4e6c04655638
--- /dev/null
+++ b/fusl/src/thread/pthread_barrier_destroy.c
@@ -0,0 +1,15 @@
+#include "pthread_impl.h"
+
+int pthread_barrier_destroy(pthread_barrier_t *b)
+{
+	if (b->_b_limit < 0) {
+		if (b->_b_lock) {
+			int v;
+			a_or(&b->_b_lock, INT_MIN);
+			while ((v = b->_b_lock) & INT_MAX)
+				__wait(&b->_b_lock, 0, v, 0);
+		}
+		__vm_wait();
+	}
+	return 0;
+}