t/Makefile: Create test-results dir for smoke target

Change the smoke target to create a test-results directory. This was
done implicitly by the test-lib before my "test-lib: Don't write
test-results when HARNESS_ACTIVE" patch, but after that smoking from
the pu branch hasn't worked.

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

t/Makefile

@@ -58,7 +58,7 @@ uname_M := $(shell sh -c 'uname -m 2>/dev/null || echo unknown')
 test-results:
 	mkdir -p test-results
 
-test-results/git-smoke.tar.gz:
+test-results/git-smoke.tar.gz: test-results
 	$(PERL_PATH) ./harness \
 		--archive="test-results/git-smoke.tar.gz" \
 		$(T)