[libc++] Implement <numbers>

Summary: Constants have 33 significant decimal digits for IEEE 754 128-bit floating-point numbers.

Reviewers: ldionne, #libc, EricWF, zoecarver, curdeius

Reviewed By: ldionne, #libc, curdeius

Differential Revision: https://reviews.llvm.org/D77505

Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 4f6c4b473c4a57ec597a201dee483204454c8a6d
diff --git a/include/version b/include/version
index 5a25047..ee78e6c 100644
--- a/include/version
+++ b/include/version
@@ -75,6 +75,7 @@
 __cpp_lib_make_reverse_iterator                         201402L <iterator>
 __cpp_lib_make_unique                                   201304L <memory>
 __cpp_lib_map_try_emplace                               201411L <map>
+__cpp_lib_math_constants                                201907L <numbers>
 __cpp_lib_math_special_functions                        201603L <cmath>
 __cpp_lib_memory_resource                               201603L <memory_resource>
 __cpp_lib_node_extract                                  201606L <map> <set> <unordered_map>
@@ -237,6 +238,7 @@
 #   define __cpp_lib_is_constant_evaluated              201811L
 # endif
 # define __cpp_lib_list_remove_return_type              201806L
+# define __cpp_lib_math_constants                       201907L
 // # define __cpp_lib_ranges                               201811L
 # define __cpp_lib_span                                 202002L
 // # define __cpp_lib_three_way_comparison                 201711L