Add more missing libc/libc++ functions

- Add sched_rr_get_interval()
- Add `unbuffer` command example
- Add more locale function stubs
- Vendor most of remaining libcxx content

third_party/libcxx/clocale

@@ -0,0 +1,55 @@
+// -*- C++ -*-
+// clang-format off
+//===--------------------------- clocale ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_CLOCALE
+#define _LIBCPP_CLOCALE
+
+/*
+    clocale synopsis
+
+Macros:
+
+    LC_ALL
+    LC_COLLATE
+    LC_CTYPE
+    LC_MONETARY
+    LC_NUMERIC
+    LC_TIME
+    NULL
+
+namespace std
+{
+
+struct lconv;
+char* setlocale(int category, const char* locale);
+lconv* localeconv();
+
+}  // std
+
+*/
+
+#include "third_party/libcxx/__config"
+#include "libc/unicode/locale.h"
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+using ::lconv;
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+using ::setlocale;
+#endif
+using ::localeconv;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif  // _LIBCPP_CLOCALE