[libc++] Mark __cpp_lib_hardware_interference_size as unimplemented. This fxes bug PR41423.

Summary:
As described in the bug report:
The commit a8b9f59e8caf378d56e8bfcecdb22184cdabf42d "Implement feature test macros using a script" added test features macros for libc++. Among others, it added `__cpp_lib_hardware_interference_size`. However, there is nothing like std::hardware_constructive_interference_size nor std::hardware_destructive_interference_size, that should be in header <new>.

* https://bugs.llvm.org/show_bug.cgi?id=41423

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D80431

Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 174322c2737d699e199db4762aaf4217305ec465
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 77c7c68..e862840 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -100,7 +100,7 @@
     ------------------------------------------------- -----------------
     ``__cpp_lib_gcd_lcm``                             ``201606L``      
     ------------------------------------------------- -----------------
-    ``__cpp_lib_hardware_interference_size``          ``201703L``      
+    ``__cpp_lib_hardware_interference_size``          *unimplemented*  
     ------------------------------------------------- -----------------
     ``__cpp_lib_has_unique_object_representations``   ``201606L``      
     ------------------------------------------------- -----------------