cmd/asm/internal: use slices.Contains

Now that Go 1.22.6 is the minimum bootstrap toolchain (cf. CL 606156),
the slices package (introduced in Go 1.21) can be used in packages built
using the bootstrap toolchain.

For #64751

Change-Id: I0115213da4b1f0a1fa0ef7ad34456fbf52e00fae
Reviewed-on: https://go-review.googlesource.com/c/go/+/611095
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Tobias Klauser <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

src/cmd/asm/internal/lex/input.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"text/scanner"
@@ -252,7 +253,7 @@ func (in *Input) macroDefinition(name string) ([]string, []Token) {
 					in.Error("bad syntax in definition for macro:", name)
 				}
 				arg := in.Stack.Text()
-				if i := lookup(args, arg); i >= 0 {
+				if slices.Contains(args, arg) {
 					in.Error("duplicate argument", arg, "in definition for macro:", name)
 				}
 				args = append(args, arg)
@@ -280,15 +281,6 @@ func (in *Input) macroDefinition(name string) ([]string, []Token) {
 	return args, tokens
 }
 
-func lookup(args []string, arg string) int {
-	for i, a := range args {
-		if a == arg {
-			return i
-		}
-	}
-	return -1
-}
-
 // invokeMacro pushes onto the input Stack a Slice that holds the macro definition with the actual
 // parameters substituted for the formals.
 // Invoking a macro does not touch the PC/line history.