Minor rewording

Author: ldionne

libcxx/docs/UserDocumentation.rst

@@ -132,9 +132,9 @@ enable or disable extended libc++ behavior.
   When this macro is defined, the standard library headers will adhere to a
   stricter policy regarding the (transitive) inclusion of other standard library
   headers, only guaranteeing to provide those definitions explicitly mandated by
-  the standard. Please notice that defining this macro might break any existing
-  codebase that implicitly relies on standard headers providing any definitions
-  not explicitly required by the standard.
+  the standard. Please notice that defining this macro might break existing codebases
+  that implicitly rely on standard headers providing definitions not explicitly
+  required by the standard.
 
   The primary motivation for this configuration macro is to improve compilation
   times. In most standard library implementations, header files include more