test: Build test object when it's really changed

It takes quite some time to build all test object but mostly we don't
need build them all.  I wanted to just 100% sure it tests correct code
by build them everytime but I realized it's annoying so change it.

Also change it to be built in the $(objdir) directory.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>

tests/Makefile

@@ -6,9 +6,13 @@ UNIT_TEST_SRC += $(wildcard $(srcdir)/cmds/*.c)
 UNIT_TEST_SRC += $(wildcard $(srcdir)/utils/*.c)
 UNIT_TEST_SRC += $(wildcard $(srcdir)/arch/$(ARCH)/*.c)
 UNIT_TEST_SRC += $(wildcard $(srcdir)/libmcount/*.c)
-UNIT_TEST_OBJ := $(patsubst %.c,%.ot,$(UNIT_TEST_SRC))
+UNIT_TEST_OBJ := $(patsubst $(srcdir)/%.c,$(objdir)/%.ot,$(UNIT_TEST_SRC))
 UNIT_TEST_OBJ := $(filter-out %-nop.ot,$(UNIT_TEST_OBJ))
 
+UNIT_TEST_OBJ_VERSION := $(objdir)/cmds/script.ot $(objdir)/cmds/tui.ot
+UNIT_TEST_OBJ_VERSION += $(objdir)/cmds/dump.ot   $(objdir)/cmds/info.ot
+UNIT_TEST_OBJ_VERSION += $(objdir)/libmcount/mcount.ot
+
 FULL_WORKER := -j $(shell getconf _NPROCESSORS_ONLN || echo 1)
 
 # these needs to be recursively expanded
@@ -32,7 +36,9 @@ test_unit: unittest
 unittest: unittest.c unittest.h $(UNIT_TEST_OBJ)
 	$(QUIET_LINK)$(CC) -o $@ $(TEST_CFLAGS) $< $(UNIT_TEST_OBJ) $(TEST_LDFLAGS)
 
-$(UNIT_TEST_OBJ): %.ot: %.c $(srcdir)/version.h
+$(UNIT_TEST_OBJ_VERSION): $(srcdir)/version.h
+
+$(UNIT_TEST_OBJ): $(objdir)/%.ot: $(srcdir)/%.c
 	$(QUIET_CC)$(CC) -o $@ -c $(TEST_CFLAGS) $<
 
 clean: