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.

libc/mem/get_current_dir_name.c

@@ -28,7 +28,7 @@
  *
  * @return pointer that must be free()'d, or NULL w/ errno
  */
-nodiscard char *get_current_dir_name(void) {
+dontdiscard char *get_current_dir_name(void) {
   const char *p;
   if ((p = getenv("PWD")) && _isabspath(p)) {
     return strdup(p);