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

fusl/src/thread/pthread_rwlock_init.c

Index: fusl/src/thread/pthread_rwlock_init.c
diff --git a/fusl/src/thread/pthread_rwlock_init.c b/fusl/src/thread/pthread_rwlock_init.c
new file mode 100644
index 0000000000000000000000000000000000000000..a2c0b478c78cf36ef7f15e4d65956e517c647221
--- /dev/null
+++ b/fusl/src/thread/pthread_rwlock_init.c
@@ -0,0 +1,8 @@
+#include "pthread_impl.h"
+
+int pthread_rwlock_init(pthread_rwlock_t *restrict rw, const pthread_rwlockattr_t *restrict a)
+{
+	*rw = (pthread_rwlock_t){0};
+	if (a) rw->_rw_shared = a->__attr[0]*128;
+	return 0;
+}