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/testlib/formatint.c

@@ -25,7 +25,7 @@
 static size_t sbufi_;
 static char sbufs_[2][256];
 
-nodiscard testonly char *testlib_formatint(intptr_t x) {
+dontdiscard testonly char *testlib_formatint(intptr_t x) {
   char *str = sbufi_ < ARRAYLEN(sbufs_) ? sbufs_[sbufi_++] : malloc(256);
   char *p = str;
   p += sprintf(p, "%ld\t(or %#lx", x, x);