cgen: fix several sort declarations (#10919)

vlib/builtin/sorting_test.v

@@ -65,3 +65,20 @@ fn test_sorting_u64s() {
 	eprintln(' a: $a')
 	assert a == [u64(9), 8, 3, 2, 1, 0]
 }
+
+struct User {
+	age  int
+	name string
+}
+
+fn g(mut users []User) {
+	users.sort(a.name > b.name)
+}
+
+fn f(mut users []User) {
+	users.sort(a.name < b.name)
+}
+
+fn z(mut users []User) {
+	users.sort(a.name < b.name)
+}

vlib/v/gen/c/array.v

@@ -244,13 +244,14 @@ fn (mut g Gen) gen_array_sort(node ast.CallExpr) {
 	if compare_fn == '' {
 		// `users.sort(a.age > b.age)`
 		// Generate a comparison function for a custom type
-		tmp_name := g.new_tmp_var()
+		tmp_name := g.new_global_tmp_var()
 		styp := g.typ(typ).trim('*')
 		compare_fn = 'compare_${tmp_name}_$styp'
 		if is_reverse {
 			compare_fn += '_reverse'
 		}
 		// Register a new custom `compare_xxx` function for qsort()
+		// TODO: move to checker
 		g.table.register_fn(name: compare_fn, return_type: ast.int_type)
 
 		if node.args.len == 0 {

vlib/v/gen/c/cgen.v

@@ -71,6 +71,7 @@ mut:
 	tmp_count              int      // counter for unique tmp vars (_tmp1, _tmp2 etc); resets at the start of each fn.
 	tmp_count2             int      // a separate tmp var counter for autofree fn calls
 	tmp_count_declarations int      // counter for unique tmp names (_d1, _d2 etc); does NOT reset, used for C declarations
+	global_tmp_count       int      // like tmp_count but global and not resetted in each function
 	is_assign_lhs          bool     // inside left part of assign expr (for array_set(), etc)
 	discard_or_result      bool     // do not safe last ExprStmt of `or` block in tmp variable to defer ongoing expr usage
 	is_void_expr_stmt      bool     // ExprStmt whos result is discarded
@@ -1004,6 +1005,11 @@ pub fn (mut g Gen) new_tmp_var() string {
 	return '_t$g.tmp_count'
 }
 
+pub fn (mut g Gen) new_global_tmp_var() string {
+	g.global_tmp_count++
+	return '_t$g.global_tmp_count'
+}
+
 pub fn (mut g Gen) new_tmp_declaration_name() string {
 	g.tmp_count_declarations++
 	return '_d$g.tmp_count_declarations'