[libc++] Implement P0401R6 (allocate_at_least)

Reviewed By: ldionne, var-const, #libc

Spies: mgorny, libcxx-commits, arichardson

Differential Revision: https://reviews.llvm.org/D122877

NOKEYCHECK=True
GitOrigin-RevId: a96443eddedc250188b5e5f2b74ae1cf2baf1472
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index e305a78..fa5dcb1 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -300,7 +300,7 @@
     -------------------------------------------------------------------
     ``__cpp_lib_adaptor_iterator_pair_constructor``   ``202106L``
     ------------------------------------------------- -----------------
-    ``__cpp_lib_allocate_at_least``                   *unimplemented*
+    ``__cpp_lib_allocate_at_least``                   ``202106L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_associative_heterogeneous_erasure``   *unimplemented*
     ------------------------------------------------- -----------------