t9700: Use Test::More->builder, not $Test::Builder::Test

t9700: Use Test::More->builder, not $Test::Builder::Test

$Test::Builder::Test was only made into an `our' variable in 0.94
released in September 2009, older distros are more likely to have 0.92
or earlier. Use the singleton Test::More->builder constructor instead.

The exit() call was also unportable to <0.94. Just output a meaningful
exit code if the ->is_passing method exists. The t9700-perl-git.sh
test only cares about stderr output, so this doesn't affect test
results when using older Test::More modules.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>