test: minor simplification to run.go

This is a little clearer, and we're about to need the .s file list in
one more place, so this will cut down on duplication.

Change-Id: I4da8bf03a0469fb97565b0841c40d505657b574e
Reviewed-on: https://go-review.googlesource.com/c/146998
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/run.go

@@ -796,14 +796,14 @@ func (t *test) run() {
 			t.err = dirErr
 			break
 		}
-		var gos []os.FileInfo
-		var asms []os.FileInfo
+		var gos []string
+		var asms []string
 		for _, file := range files {
 			switch filepath.Ext(file.Name()) {
 			case ".go":
-				gos = append(gos, file)
+				gos = append(gos, filepath.Join(longdir, file.Name()))
 			case ".s":
-				asms = append(asms, file)
+				asms = append(asms, filepath.Join(longdir, file.Name()))
 			}
 
 		}
@@ -812,9 +812,7 @@ func (t *test) run() {
 		if len(asms) > 0 {
 			cmd = append(cmd, "-asmhdr", "go_asm.h")
 		}
-		for _, file := range gos {
-			cmd = append(cmd, filepath.Join(longdir, file.Name()))
-		}
+		cmd = append(cmd, gos...)
 		_, err := runcmd(cmd...)
 		if err != nil {
 			t.err = err
@@ -823,9 +821,7 @@ func (t *test) run() {
 		objs = append(objs, "go.o")
 		if len(asms) > 0 {
 			cmd = []string{goTool(), "tool", "asm", "-e", "-I", ".", "-o", "asm.o"}
-			for _, file := range asms {
-				cmd = append(cmd, filepath.Join(longdir, file.Name()))
-			}
+			cmd = append(cmd, asms...)
 			_, err = runcmd(cmd...)
 			if err != nil {
 				t.err = err