Import C++ Standard Template Library

You can now use the hardest fastest and most dangerous language there is
with Cosmopolitan. So far about 75% of LLVM libcxx has been added. A few
breaking changes needed to be made to help this go smoothly.

- Rename nothrow to dontthrow
- Rename nodiscard to dontdiscard
- Add some libm functions, e.g. lgamma, nan, etc.
- Change intmax_t from int128 to int64 like everything else
- Introduce %jjd formatting directive for int128_t
- Introduce strtoi128(), strtou128(), etc.
- Rename bsrmax() to bsr128()

Some of the templates that should be working currently are std::vector,
std::string, std::map, std::set, std::deque, etc.

third_party/libcxx/ctime

@@ -0,0 +1,81 @@
+// -*- C++ -*-
+//===---------------------------- ctime -----------------------------------===//
+//
+// 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_CTIME
+#define _LIBCPP_CTIME
+
+/*
+    ctime synopsis
+
+Macros:
+
+    NULL
+    CLOCKS_PER_SEC
+    TIME_UTC // C++17
+    
+namespace std
+{
+
+Types:
+
+    clock_t
+    size_t
+    time_t
+    tm
+    timespec // C++17
+    
+clock_t clock();
+double difftime(time_t time1, time_t time0);
+time_t mktime(tm* timeptr);
+time_t time(time_t* timer);
+char* asctime(const tm* timeptr);
+char* ctime(const time_t* timer);
+tm*    gmtime(const time_t* timer);
+tm* localtime(const time_t* timer);
+size_t strftime(char* restrict s, size_t maxsize, const char* restrict format,
+                const tm* restrict timeptr);
+int timespec_get( struct timespec *ts, int base); // C++17
+}  // std
+
+*/
+
+#include "third_party/libcxx/__config"
+#include "libc/isystem/time.h"
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+using ::clock_t;
+using ::size_t;
+using ::time_t;
+using ::tm;
+#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_C11_FEATURES)
+using ::timespec;
+#endif
+using ::clock;
+using ::difftime;
+using ::mktime;
+using ::time;
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+using ::asctime;
+using ::ctime;
+using ::gmtime;
+using ::localtime;
+#endif
+using ::strftime;
+#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_TIMESPEC_GET)
+using ::timespec_get;
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif  // _LIBCPP_CTIME