perf/run: learn about perf.codespeedOutput

Let's make it possible to set in a config file the output
format (regular or codespeed) of the perf tests.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/run

@@ -144,10 +144,15 @@ run_subsection () {
 		set -- . "$@"
 	fi
 
+	codespeed_opt=
+	test "$GIT_PERF_CODESPEED_OUTPUT" = "true" && codespeed_opt="--codespeed"
+
 	run_dirs "$@"
-	./aggregate.perl "$@"
+	./aggregate.perl $codespeed_opt "$@"
 }
 
+get_var_from_env_or_config "GIT_PERF_CODESPEED_OUTPUT" "perf" "codespeedOutput" "--bool"
+
 cd "$(dirname $0)"
 . ../../GIT-BUILD-OPTIONS