[libc++][ranges] Sets ranges feature-test macro.
D131234 marked the ranges papers as complete, but it didn't set the
feature-test macro.
Reviewed By: ldionne, var-const, #libc
Differential Revision: https://reviews.llvm.org/D131326
NOKEYCHECK=True
GitOrigin-RevId: 195287d90afb1b97a0fb869da501370e7c3e67c6
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 9aa183a..e5a06dc 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -262,7 +262,7 @@
------------------------------------------------- -----------------
``__cpp_lib_polymorphic_allocator`` *unimplemented*
------------------------------------------------- -----------------
- ``__cpp_lib_ranges`` *unimplemented*
+ ``__cpp_lib_ranges`` ``201811L``
------------------------------------------------- -----------------
``__cpp_lib_remove_cvref`` ``201711L``
------------------------------------------------- -----------------