[expr.{add,alignof,sizeof}] Avoid using "defined" for typedefs

Author: frederick-vs-ja

source/expressions.tex

@@ -5154,7 +5154,7 @@
 \begin{note}
 A \keyword{sizeof} expression
 is an integral constant expression\iref{expr.const}.
-The type \tcode{std::size_t} is defined in the standard header
+The \grammarterm{typedef-name} \tcode{std::size_t} is declared in the standard header
 \libheader{cstddef}\iref{cstddef.syn,support.types.layout}.
 \end{note}
 
@@ -5173,7 +5173,7 @@
 \begin{note}
 An \keyword{alignof} expression
 is an integral constant expression\iref{expr.const}.
-The type \tcode{std::size_t} is defined in the standard header
+The \grammarterm{typedef-name} \tcode{std::size_t} is declared in the standard header
 \libheader{cstddef}\iref{cstddef.syn,support.types.layout}.
 \end{note}
 
@@ -6435,7 +6435,7 @@
 \indextext{comparison!undefined pointer}%
 When two pointer expressions \tcode{P} and \tcode{Q} are subtracted,
 the type of the result is an \impldef{type of \tcode{ptrdiff_t}} signed
-integral type; this type shall be the same type that is defined as
+integral type; this type shall be the same type that is named by
 \tcode{std::ptrdiff_t} in the \libheader{cstddef}
 header\iref{support.types.layout}.
 \begin{itemize}