selftests: memfd: Stop unnecessary rebuilds

Instead of explicitly running the compiler, add dependencies and take
advantage of implicit rules to build only as necessary.
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/memfd/Makefile

@@ -4,16 +4,16 @@ CFLAGS += -I../../../../include/uapi/
 CFLAGS += -I../../../../include/
 CFLAGS += -I../../../../usr/include/
 
-all:
-	$(CC) $(CFLAGS) memfd_test.c -o memfd_test
-
 TEST_PROGS := memfd_test
 
+all: $(TEST_PROGS)
+
 include ../lib.mk
 
-build_fuse:
-	$(CC) $(CFLAGS) fuse_mnt.c `pkg-config fuse --cflags --libs` -o fuse_mnt
-	$(CC) $(CFLAGS) fuse_test.c -o fuse_test
+build_fuse: fuse_mnt fuse_test
+
+fuse_mnt.o: CFLAGS += $(shell pkg-config fuse --cflags)
+fuse_mnt: LDFLAGS += $(shell pkg-config fuse --libs)
 
 run_fuse: build_fuse
 	@./run_fuse_test.sh || echo "fuse_test: [FAIL]"