disable post-checkout test on Cygwin

It is broken because of the tricks we have to play with
lstat to get the bearable perfomance out of the call.
Sadly, it disables access to Cygwin's executable attribute,
which Windows filesystems do not have at all.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5403-post-checkout-hook.sh

@@ -71,6 +71,7 @@ test_expect_success 'post-checkout receives the right args when not switching br
         test $old = $new -a $flag = 0
 '
 
+if test "$(git config --bool core.filemode)" = true; then
 mkdir -p templates/hooks
 cat >templates/hooks/post-checkout <<'EOF'
 #!/bin/sh
@@ -82,5 +83,6 @@ test_expect_success 'post-checkout hook is triggered by clone' '
 	git clone --template=templates . clone3 &&
 	test -f clone3/.git/post-checkout.args
 '
+fi
 
 test_done