Makefile: Split out the untested functions target

Change the coverage-report target so that it doesn't generate the
coverage-untested-functions file by default. I'm adding more targets
for doing various things with the gcov files, and they shouldn't all
run by default.

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

Makefile

@@ -2312,6 +2312,8 @@ coverage-report:
 	$(QUIET_GCOV)for dir in $(object_dirs); do \
 		gcov $(GCOVFLAGS) --object-directory=$$dir $$dir*.c || exit; \
 	done
+
+coverage-untested-functions: coverage-report
 	grep '^function.*called 0 ' *.c.gcov \
 		| sed -e 's/\([^:]*\)\.gcov: *function \([^ ]*\) called.*/\1: \2/' \
 		> coverage-untested-functions