Makefile: Cover more files with make check

After the builtin/ move 'make check' doesn't cover the builtin/
directory. We could just add builtin/*.c but lets just use GIT_OBJS
instead so we cover future movement of the source files.

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -2176,7 +2176,7 @@ check-sha1:: test-sha1$X
 check: common-cmds.h
 	if sparse; \
 	then \
-		for i in *.c; \
+		for i in $(patsubst %.o, %.c, $(GIT_OBJS)); \
 		do \
 			sparse $(ALL_CFLAGS) $(SPARSE_FLAGS) $$i || exit; \
 		done; \