perf jvmti: Link against tools/lib/string.o to have weak strlcpy()

That is needed in systems such some S/390 distros.

  $ readelf -s /tmp/build/perf/jvmti/jvmti-in.o | grep strlcpy
	452: 0000000000002990   125 FUNC    WEAK   DEFAULT  119 strlcpy
  $

Thanks to Jiri Olsa for fixing up my initial stab at this, I forgot how
Makefiles are picky about spaces versus tabs.
Reported-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andreas Krebbel <krebbel@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Sergey Melnikov <melnikov.sergey.v@gmail.com>
Link: https://lkml.kernel.org/n/tip-x8vg9sffgb2t1tzqmhkrulh7@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/jvmti/Build

 jvmti-y += libjvmti.o
 jvmti-y += jvmti_agent.o
 
+# For strlcpy
+jvmti-y += libstring.o
+
 CFLAGS_jvmti         = -fPIC -DPIC -I$(JDIR)/include -I$(JDIR)/include/linux
 CFLAGS_REMOVE_jvmti  = -Wmissing-declarations
 CFLAGS_REMOVE_jvmti += -Wstrict-prototypes
 CFLAGS_REMOVE_jvmti += -Wextra
 CFLAGS_REMOVE_jvmti += -Wwrite-strings
+
+CFLAGS_libstring.o += -Wno-unused-parameter -DETC_PERFCONFIG="BUILD_STR($(ETC_PERFCONFIG_SQ))"
+
+$(OUTPUT)jvmti/libstring.o: ../lib/string.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)