Fixup missing \impldef for bad_expected_access::what

Author: eisenwave

source/utilities.tex

@@ -7383,7 +7383,7 @@
 \begin{itemdescr}
 \pnum
 \returns
-An implementation-defined \ntbs,
+An \impldef{return value of \tcode{bad_expected_access<E>::what}} \ntbs,
 which during constant evaluation is encoded with
 the ordinary literal encoding\iref{lex.ccon}.
 \end{itemdescr}
@@ -7416,7 +7416,7 @@
 \begin{itemdescr}
 \pnum
 \returns
-An implementation-defined \ntbs,
+An \impldef{return value of \tcode{bad_expected_access<void>::what}} \ntbs,
 which during constant evaluation is encoded with
 the ordinary literal encoding\iref{lex.ccon}.
 \end{itemdescr}