test: avoid unnamed parameter in function type template argument

Author: JohelEGP

regression-tests/pure2-last-use.cpp2

@@ -270,9 +270,9 @@ issue_857_6: @struct type = {
 
 issue_857_4: @struct type = {
    f: std::add_pointer_t<()->int>;
-   g: std::add_pointer_t<(_:int)->int>;
+   g: std::add_pointer_t<(x:int)->int>;
   mf: std::move_only_function<()->int>;
-  mg: std::move_only_function<(_:int)->int>;
+  mg: std::move_only_function<(x:int)->int>;
 //   h0: (move this) = _ = mf();
 //   h1: (move this) = _ = this.mf();
 //   h2: (move this, that) = _ = that.mf();
@@ -770,7 +770,7 @@ issue_884: () = {
 issue_888_0: (copy r: std::string, copy size: int) = {
   _ = r.size();
 }
-issue_888_1: (copy _: std::string, copy size: std::move_only_function<(_:int)->int>) = {
+issue_888_1: (copy _: std::string, copy size: std::move_only_function<(x:int)->int>) = {
   _ = 0.size();
 }
 
@@ -787,7 +787,7 @@ issue_962: (s: ::std::string) = {
 
 draw: () = {
   pos := 0;
-  vertex: std::move_only_function<(_:int)->int> = ();
+  vertex: std::move_only_function<(x:int)->int> = ();
   _ = (pos).vertex();
 }