selftests/landlock: Build without static libraries

The only (forced) static test binary doesn't depend on libcap.  Because
using -lcap on systems that don't have such static library would fail
(e.g. on Arch Linux), let's be more specific and require only dynamic
libcap linking.

Fixes: a5254052 ("selftests/landlock: Fix out-of-tree builds")
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20221019200536.2771316-1-mic@digikod.net

tools/testing/selftests/landlock/Makefile

@@ -3,7 +3,6 @@
 # First run: make -C ../../../.. headers_install
 
 CFLAGS += -Wall -O2 $(KHDR_INCLUDES)
-LDLIBS += -lcap
 
 LOCAL_HDRS += common.h
 
@@ -13,10 +12,12 @@ TEST_GEN_PROGS := $(src_test:.c=)
 
 TEST_GEN_PROGS_EXTENDED := true
 
-# Static linking for short targets:
+# Short targets:
+$(TEST_GEN_PROGS): LDLIBS += -lcap
 $(TEST_GEN_PROGS_EXTENDED): LDFLAGS += -static
 
 include ../lib.mk
 
-# Static linking for targets with $(OUTPUT)/ prefix:
+# Targets with $(OUTPUT)/ prefix:
+$(TEST_GEN_PROGS): LDLIBS += -lcap
 $(TEST_GEN_PROGS_EXTENDED): LDFLAGS += -static