cmd/cgo/internal/test: don't skip some tests on musl

They reportedly work at least as of Alpine 3.18.

Fixes #39857

Change-Id: I6a249d61d33e467bf32e8c250f870fc261b90941
Reviewed-on: https://go-review.googlesource.com/c/go/+/563096
Auto-Submit: Ian Lance Taylor <[email protected]>
Commit-Queue: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

src/cmd/cgo/internal/test/cgo_linux_test.go

@@ -7,7 +7,6 @@
 package cgotest
 
 import (
-	"os"
 	"runtime"
 	"testing"
 )
@@ -16,30 +15,18 @@ func TestSetgid(t *testing.T) {
 	if runtime.GOOS == "android" {
 		t.Skip("unsupported on Android")
 	}
-	if _, err := os.Stat("/etc/alpine-release"); err == nil {
-		t.Skip("setgid is broken with musl libc - go.dev/issue/39857")
-	}
 	testSetgid(t)
 }
 
 func TestSetgidStress(t *testing.T) {
 	if runtime.GOOS == "android" {
 		t.Skip("unsupported on Android")
 	}
-	if _, err := os.Stat("/etc/alpine-release"); err == nil {
-		t.Skip("setgid is broken with musl libc - go.dev/issue/39857")
-	}
 	testSetgidStress(t)
 }
 
 func Test1435(t *testing.T) { test1435(t) }
 func Test6997(t *testing.T) { test6997(t) }
-
-func Test9400(t *testing.T) {
-	if _, err := os.Stat("/etc/alpine-release"); err == nil {
-		t.Skip("setgid is broken with musl libc - go.dev/issue/39857")
-	}
-	test9400(t)
-}
+func Test9400(t *testing.T) { test9400(t) }
 
 func TestBuildID(t *testing.T) { testBuildID(t) }