[exec.spawn.future] Rename expos-only member to "variant-t"

Author: tkoeppe

source/exec.tex

@@ -5199,8 +5199,8 @@
 
   template<class... Sigs>
   struct @\exposid{spawn-future-state-base}@<completion_signatures<Sigs...>> {  // \expos
-    using @\exposid{variant_t}@ = @\seebelow@;                                    // \expos
-    @\exposid{variant_t}@ @\exposid{result}@;                                               // \expos
+    using @\exposid{variant-t}@ = @\seebelow@;                                    // \expos
+    @\exposid{variant-t}@ @\exposid{result}@;                                               // \expos
     virtual void @\exposid{complete}@() noexcept = 0;                           // \expos
   };
 }
@@ -5221,13 +5221,13 @@
 in every parameter pack \tcode{Args}
 in every completion signature \tcode{Tag(Args...)}
 in \tcode{Sigs} then
-\exposid{variant_t} denotes the type
+\exposid{variant-t} denotes the type
 \tcode{variant<monostate, tuple<set_stopped_t>, \placeholder{as-tuple}<Sigs>...>},
 except with duplicate types removed.
 
 \item
 Otherwise
-\exposid{variant_t} denotes the type
+\exposid{variant-t} denotes the type
 \tcode{variant<monostate, tuple<set_stopped_t>, tuple<set_error_t, exception_ptr>, \placeholder{as-tuple}<Sigs>...>},
 except with duplicate types removed.
 \end{itemize}