[libc++] [P1612] Add missing feature-test macro __cpp_lib_endian.

Thanks to Marek Kurdej for the patch.

Differential Revision: https://reviews.llvm.org/D70221

Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 8b77a3a0f4ef8c2cda3a0437fe54e2c2ecef1b17
diff --git a/include/version b/include/version
index fe9cfed..2abc71e 100644
--- a/include/version
+++ b/include/version
@@ -43,6 +43,7 @@
 __cpp_lib_constexpr_swap_algorithms                     201806L <algorithm>
 __cpp_lib_destroying_delete                             201806L <new>
 __cpp_lib_enable_shared_from_this                       201603L <memory>
+__cpp_lib_endian                                        201907L <bit>
 __cpp_lib_erase_if                                      201811L <string> <deque> <forward_list>
                                                                 <list> <vector> <map>
                                                                 <set> <unordered_map> <unordered_set>
@@ -223,6 +224,7 @@
 # if _LIBCPP_STD_VER > 17 && defined(__cpp_impl_destroying_delete) && __cpp_impl_destroying_delete >= 201806L
 #   define __cpp_lib_destroying_delete                  201806L
 # endif
+# define __cpp_lib_endian                               201907L
 # define __cpp_lib_erase_if                             201811L
 // # define __cpp_lib_generic_unordered_lookup             201811L
 # define __cpp_lib_interpolate                          201902L