[dcl.attr.nodiscard], [diff.cpp17.dcl.dcl] Fix grammar/usage

Author: opensdh

source/compatibility.tex

@@ -1927,7 +1927,7 @@
 
 \diffref{dcl.typedef}
 \change Unnamed classes with a typedef name for linkage purposes
-can only contain C-compatible constructs.
+can contain only C-compatible constructs.
 \rationale Necessary for implementability.
 \effect Valid C++ 2017 code may be ill-formed in this International Standard.
 \begin{codeblock}

source/declarations.tex

@@ -8991,7 +8991,7 @@
 in a function declaration or to the declaration of a class or enumeration.
 It shall appear at most once in each \grammarterm{attribute-list}.
 An \grammarterm{attribute-argument-clause} may be present
-and, if present, it shall have the form:
+and, if present, shall have the form:
 
 \begin{ncbnf}
 \terminal{(} string-literal \terminal{)}