lib: c: pthread: implement per-thread errno storage

lib/libc/pthread/thread/errno.c

@@ -0,0 +1,12 @@
+#include "pthread.h"
+
+#include <mango/log.h>
+#include <pthread.h>
+#include <stdio.h>
+
+int *__errno_location(void)
+{
+	struct __pthread *self = pthread_self();
+	kern_logf("using pthread errno %p", &self->thr_errno);
+	return &self->thr_errno;
+}