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/__undef_macros

@@ -0,0 +1,33 @@
+// -*- C++ -*-
+//===------------------------ __undef_macros ------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+
+#ifdef min
+#if !defined(_LIBCPP_DISABLE_MACRO_CONFLICT_WARNINGS)
+#if defined(_LIBCPP_WARNING)
+_LIBCPP_WARNING("macro min is incompatible with C++.  Try #define NOMINMAX "
+                "before any Windows header. #undefing min")
+#else
+#warning: macro min is incompatible with C++.  #undefing min
+#endif
+#endif
+#undef min
+#endif
+
+#ifdef max
+#if !defined(_LIBCPP_DISABLE_MACRO_CONFLICT_WARNINGS)
+#if defined(_LIBCPP_WARNING)
+_LIBCPP_WARNING("macro max is incompatible with C++.  Try #define NOMINMAX "
+                "before any Windows header. #undefing max")
+#else
+#warning: macro max is incompatible with C++.  #undefing max
+#endif
+#endif
+#undef max
+#endif