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

fusl/src/stdio/__lockfile.c

Index: fusl/src/stdio/__lockfile.c
diff --git a/fusl/src/stdio/__lockfile.c b/fusl/src/stdio/__lockfile.c
new file mode 100644
index 0000000000000000000000000000000000000000..9d967d6eb8860c0522b9fcd8505d6e52fad19b6b
--- /dev/null
+++ b/fusl/src/stdio/__lockfile.c
@@ -0,0 +1,28 @@
+#include "stdio_impl.h"
+#include "pthread_impl.h"
+
+int __lockfile(FILE *f)
+{
+	int owner, tid = __pthread_self()->tid;
+	if (f->lock == tid)
+		return 0;
+	while ((owner = a_cas(&f->lock, 0, tid)))
+		__wait(&f->lock, &f->waiters, owner, 1);
+	return 1;
+}
+
+void __unlockfile(FILE *f)
+{
+	a_store(&f->lock, 0);
+
+	/* The following read is technically invalid under situations
+	 * of self-synchronized destruction. Another thread may have
+	 * called fclose as soon as the above store has completed.
+	 * Nonetheless, since FILE objects always live in memory
+	 * obtained by malloc from the heap, it's safe to assume
+	 * the dereferences below will not fault. In the worst case,
+	 * a spurious syscall will be made. If the implementation of
+	 * malloc changes, this assumption needs revisiting. */
+
+	if (f->waiters) __wake(&f->lock, 1, 1);
+}