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/mbedtls/formatclientciphers.c

@@ -25,7 +25,7 @@
  * Returns string of joined list of first 𝑘 client preferred ciphers.
  * @return string that must be free'd, or null if none set
  */
-nodiscard char *FormatSslClientCiphers(const mbedtls_ssl_context *ssl) {
+dontdiscard char *FormatSslClientCiphers(const mbedtls_ssl_context *ssl) {
   int i;
   char *b = 0;
   for (i = 0; i < ARRAYLEN(ssl->client_ciphers); ++i) {