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

fusl/src/thread/pthread_barrier_init.c

Index: fusl/src/thread/pthread_barrier_init.c
diff --git a/fusl/src/thread/pthread_barrier_init.c b/fusl/src/thread/pthread_barrier_init.c
new file mode 100644
index 0000000000000000000000000000000000000000..4c3cb28d44c36b04fe6f136af47952fb4840e311
--- /dev/null
+++ b/fusl/src/thread/pthread_barrier_init.c
@@ -0,0 +1,8 @@
+#include "pthread_impl.h"
+
+int pthread_barrier_init(pthread_barrier_t *restrict b, const pthread_barrierattr_t *restrict a, unsigned count)
+{
+	if (count-1 > INT_MAX-1) return EINVAL;
+	*b = (pthread_barrier_t){ ._b_limit = count-1 | (a?a->__attr:0) };
+	return 0;
+}