darwin: tests/defaults: fix unix.Getdents build failureHEADmaster

Error was:

+ go test -c -tags without_openssl -o /dev/null github.com/rfjakob/gocryptfs/v2/tests/defaults
Error: tests/defaults/main_test.go:532:17: undefined: unix.Getdents
Error: tests/defaults/main_test.go:538:16: undefined: unix.Getdents
Error: tests/defaults/main_test.go:549:16: undefined: unix.Getdents

1 files changed, 9 insertions, 0 deletions

diff --git a/tests/defaults/getdents_linux.go b/tests/defaults/getdents_linux.go
new file mode 100644
index 0000000..57956ce
--- /dev/null
+++ b/tests/defaults/getdents_linux.go
@@ -0,0 +1,9 @@
+package defaults
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+func getdents(fd int, buf []byte) (int, error) {
+	return unix.Getdents(fd, buf)
+}