[libc++] implement 'std::generator'

Author: xiaoyang-sde

libcxx/utils/libcxx/header_information.py

@@ -165,7 +165,6 @@ def __hash__(self) -> int:
 headers_not_available = list(map(Header, [
     "debugging",
     "flat_set",
-    "generator",
     "hazard_pointer",
     "inplace_vector",
     "linalg",