test: change index.go to test size of int, not GOARCH == "amd64"

Fixes the test to work correctly on other platforms with
64-bit ints, like Alpha.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6822099

test/index.go

@@ -13,7 +13,7 @@ import (
 	"bufio"
 	"fmt"
 	"os"
-	"runtime"
+	"unsafe"
 )
 
 const prolog = `
@@ -214,9 +214,10 @@ func main() {
 				// the next pass from running.
 				// So run it as a separate check.
 				thisPass = 1
-			} else if a == "s" && n == "" && (i == "i64big" || i == "i64bigger") && runtime.GOARCH == "amd64" {
-				// On amd64, these huge numbers do fit in an int, so they are not
-				// rejected at compile time.
+			} else if a == "s" && n == "" && (i == "i64big" || i == "i64bigger") && unsafe.Sizeof(int(0)) > 4 {
+				// If int is 64 bits, these huge
+				// numbers do fit in an int, so they
+				// are not rejected at compile time.
 				thisPass = 0
 			} else {
 				thisPass = 2