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

fusl/src/thread/__lock.c

Index: fusl/src/thread/__lock.c
diff --git a/fusl/src/thread/__lock.c b/fusl/src/thread/__lock.c
new file mode 100644
index 0000000000000000000000000000000000000000..0874c04a4c0a81a9fa0dc032479ec18cec81d8aa
--- /dev/null
+++ b/fusl/src/thread/__lock.c
@@ -0,0 +1,15 @@
+#include "pthread_impl.h"
+
+void __lock(volatile int *l)
+{
+	if (libc.threads_minus_1)
+		while (a_swap(l, 1)) __wait(l, l+1, 1, 1);
+}
+
+void __unlock(volatile int *l)
+{
+	if (l[0]) {
+		a_store(l, 0);
+		if (l[1]) __wake(l, 1, 1);
+	}
+}