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

fusl/src/thread/pthread_getspecific.c

Index: fusl/src/thread/pthread_getspecific.c
diff --git a/fusl/src/thread/pthread_getspecific.c b/fusl/src/thread/pthread_getspecific.c
new file mode 100644
index 0000000000000000000000000000000000000000..d9342a560f7bc6c9341b27911ae353d03a78fb1f
--- /dev/null
+++ b/fusl/src/thread/pthread_getspecific.c
@@ -0,0 +1,11 @@
+#include "pthread_impl.h"
+#include <threads.h>
+
+static void *__pthread_getspecific(pthread_key_t k)
+{
+	struct pthread *self = __pthread_self();
+	return self->tsd[k];
+}
+
+weak_alias(__pthread_getspecific, pthread_getspecific);
+weak_alias(__pthread_getspecific, tss_get);