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

fusl/src/thread/pthread_equal.c

Index: fusl/src/thread/pthread_equal.c
diff --git a/fusl/src/thread/pthread_equal.c b/fusl/src/thread/pthread_equal.c
new file mode 100644
index 0000000000000000000000000000000000000000..7c31482af3f8fec7710d0e995ef8d40cf149ebe4
--- /dev/null
+++ b/fusl/src/thread/pthread_equal.c
@@ -0,0 +1,11 @@
+#include <pthread.h>
+#include <threads.h>
+#include "libc.h"
+
+static int __pthread_equal(pthread_t a, pthread_t b)
+{
+	return a==b;
+}
+
+weak_alias(__pthread_equal, pthread_equal);
+weak_alias(__pthread_equal, thrd_equal);