selftests/bpf: fix broken build, take 2

Merge of 'linux-kselftest-4.11-rc1':

1. Partially removed use of 'test_objs' target, breaking force rebuild of
BPFOBJ, introduced in commit d498f871 ("bpf: Rebuild bpf.o for any
dependency update").

  Update target so dependency on BPFOBJ is restored.

2. Introduced commit 2047f1d8 ("selftests: Fix the .c linking rule")
which fixes order of LDLIBS.

  Commit d02d8986 ("bpf: Always test unprivileged programs") added
libcap dependency into CFLAGS. Use LDLIBS instead to fix linking of
test_verifier.

3. Introduced commit d83c3ba0 ("selftests: Fix selftests build to
just build, not run tests").

  Reordering the Makefile allows us to remove the 'all' target.

Tested both:
    selftests/bpf$ make
and
    selftests$ make TARGETS=bpf
on Ubuntu 16.04.2.
Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/Makefile

 LIBDIR := ../../../lib
-BPFOBJ := $(LIBDIR)/bpf/bpf.o
+BPFDIR := $(LIBDIR)/bpf
 
-CFLAGS += -Wall -O2 -lcap -I../../../include/uapi -I$(LIBDIR) $(BPFOBJ)
+CFLAGS += -Wall -O2 -I../../../include/uapi -I$(LIBDIR)
+LDLIBS += -lcap
 
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map
 
 TEST_PROGS := test_kmod.sh
 
-all: $(TEST_GEN_PROGS)
+include ../lib.mk
+
+BPFOBJ := $(OUTPUT)/bpf.o
+
+$(TEST_GEN_PROGS): $(BPFOBJ)
 
-.PHONY: all clean force
+.PHONY: force
 
 # force a rebuild of BPFOBJ when its dependencies are updated
 force:
 
 $(BPFOBJ): force
-	$(MAKE) -C $(dir $(BPFOBJ))
-
-$(test_objs): $(BPFOBJ)
-
-include ../lib.mk
+	$(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/