Apply suggestions from code review

Author: ldionne

libcxx/docs/VendorDocumentation.rst

@@ -596,8 +596,8 @@ libc++'s ABI guarantees
 
 Libc++ provides several ABI guarantees, which are documented :ref:`here <ABIGuarantees>`.
 
-Availability Markups
-====================
+Availability Markup
+===================
 
 Libc++ is shipped by various vendors. In particular, it is used as a system library on macOS, iOS and other Apple
 platforms. In order for users to be able to compile a binary that is intended to be deployed to an older version of a
@@ -615,7 +615,6 @@ the symbols when actually trying to launch the program on macOS 10.13. To turn t
 declarations are annotated with when they were introduced, and the compiler can produce a diagnostic if the program
 references something that isn't available on the deployment target.
 
-
 This mechanism is general in nature, and any vendor can add their markup to the library (see below). Whenever a new
 feature is added that requires support in the shared library, two macros are added below to allow marking the feature as
 unavailable:

libcxx/include/__configuration/availability.h

@@ -20,7 +20,7 @@
 // This file defines a framework that can be used by vendors to encode the version of an operating system that various
 // features of libc++ has been shipped in. This is primarily intended to allow safely deploying an executable built with
 // a new version of the library on a platform containing an older version of the built library.
-// Detailed documentation for this can be found at https://libcxx.llvm.org/VendorDocumentation.html#availability-markups
+// Detailed documentation for this can be found at https://libcxx.llvm.org/VendorDocumentation.html#availability-markup
 
 // Availability markup is disabled when building the library, or when a non-Clang
 // compiler is used because only Clang supports the necessary attributes.