cmd/cgo: use strings.Contains instead of strings.Index

Change-Id: Iaa623dae50ccae36ad44af25899c6453b6108046
Reviewed-on: https://go-review.googlesource.com/c/go/+/435944
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>

Author: cuiweixie

src/cmd/cgo/out.go

@@ -427,7 +427,7 @@ func checkImportSymName(s string) {
 			fatalf("dynamic symbol %q contains unsupported character", s)
 		}
 	}
-	if strings.Index(s, "//") >= 0 || strings.Index(s, "/*") >= 0 {
+	if strings.Contains(s, "//") || strings.Contains(s, "/*") {
 		fatalf("dynamic symbol %q contains Go comment")
 	}
 }