[atomics.alias] Use "declare" for typedef-names

Author: frederick-vs-ja

source/threads.tex

@@ -2857,10 +2857,10 @@
 \pnum
 The type aliases \tcode{atomic_int$N$_t}, \tcode{atomic_uint$N$_t},
 \tcode{atomic_intptr_t}, and \tcode{atomic_uintptr_t}
-are defined if and only if
+are declared if and only if
 \tcode{int$N$_t}, \tcode{uint$N$_t},
 \tcode{intptr_t}, and \tcode{uintptr_t}
-are defined, respectively.
+are declared, respectively.
 
 \pnum
 \indexlibraryglobal{atomic_signed_lock_free}%