t3700-add: do not check working tree file mode without POSIXPERM

A recently introduced test checks the result of 'git status' after
setting the executable bit on a file. This check does not yield the
expected result when the filesystem does not support the executable
bit.

What we care about is that a file added with "--chmod=+x" has
executable bit in the index and that "--chmod=+x" (or any other
options for that matter) does not muck with working tree files.
The former is tested by other existing tests, so let's check the
latter more explicitly and only under POSIXPERM prerequisite.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3700-add.sh

@@ -361,13 +361,11 @@ test_expect_success 'git add --chmod=[+-]x changes index with already added file
 	test_mode_in_index 100644 xfoo3
 '
 
-test_expect_success 'file status is changed after git add --chmod=+x' '
-	echo "AM foo4" >expected &&
+test_expect_success POSIXPERM 'git add --chmod=[+-]x does not change the working tree' '
 	echo foo >foo4 &&
 	git add foo4 &&
 	git add --chmod=+x foo4 &&
-	git status -s foo4 >actual &&
-	test_cmp expected actual
+	! test -x foo4
 '
 
 test_expect_success 'no file status change if no pathspec is given' '