[cpp.predefined,namespace.future,version.syn] Replace 'C++' with 'this document'

Fixes ISO/CS comment (C++23 proof)

Author: jensmaurer

source/preprocessor.tex

@@ -1704,15 +1704,15 @@
 \xname{cplusplus}\\
 The integer literal \tcode{\cppver}.
 \begin{note}
-Future revisions of \Cpp{} will
+Future revisions of this document will
 replace the value of this macro with a greater value.
 \end{note}
 
 \item The names listed in \tref{cpp.predefined.ft}.\\
 The macros defined in \tref{cpp.predefined.ft} shall be defined to
 the corresponding integer literal.
 \begin{note}
-Future revisions of \Cpp{} might replace
+Future revisions of this document might replace
 the values of these macros with greater values.
 \end{note}
 

source/support.tex

@@ -546,7 +546,7 @@
 after inclusion of any member of the set of library headers
 indicated in the corresponding comment in this synopsis.
 \begin{note}
-Future revisions of \Cpp{} might replace
+Future revisions of this document might replace
 the values of these macros with greater values.
 \end{note}