t6006: don't use iconv(1) without ICONV prereq

Two tests in t6006 depend on the iconv(1) prerequisite to reencode a
commit message. This executable may not even exist though in case the
prereq is not set, which will cause the tests to fail.

Fix this by using UTF-8 instead when the prereq is not set.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

t/t6006-rev-list-format.sh

@@ -378,15 +378,23 @@ test_expect_success 'rev-list %C(auto,...) respects --color' '
 	test_cmp expect actual
 '
 
-iconv -f utf-8 -t $test_encoding > commit-msg <<EOF
-Test printing of complex bodies
+test_expect_success 'setup complex body' '
+	message=$(cat <<-EOF
+	Test printing of complex bodies
 
-This commit message is much longer than the others,
-and it will be encoded in $test_encoding. We should therefore
-include an ISO8859 character: ¡bueno!
-EOF
+	This commit message is much longer than the others,
+	and it will be encoded in $test_encoding. We should therefore
+	include an ISO8859 character: ¡bueno!
+	EOF
+	) &&
+
+	if test_have_prereq ICONV
+	then
+		echo "$message" | iconv -f utf-8 -t $test_encoding >commit-msg
+	else
+		echo "$message" >commit-msg
+	fi &&
 
-test_expect_success 'setup complex body' '
 	git config i18n.commitencoding $test_encoding &&
 	echo change2 >foo && git commit -a -F commit-msg &&
 	head3=$(git rev-parse --verify HEAD) &&
@@ -448,7 +456,12 @@ test_expect_success 'setup expected messages (for test %b)' '
 	commit $head2
 	commit $head1
 	EOF
-	iconv -f utf-8 -t $test_encoding expected.utf-8 >expected.ISO8859-1
+	if test_have_prereq ICONV
+	then
+		iconv -f utf-8 -t $test_encoding expected.utf-8 >expected.ISO8859-1
+	else
+		cp expected.utf-8 expected.ISO8859-1
+	fi
 '
 
 test_format complex-body %b <expected.ISO8859-1