tools lib subcmd: Use str_error_r()

To make it portable to non-glibc systems, that follow the XSI variant
instead of the GNU specific one that gets in place when _GNU_SOURCE is
defined.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-bozcszy93tpgw9ad6qm3dhpx@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/objtool/Build b/tools/objtool/Build
index 0e89258..2457916 100644
--- a/tools/objtool/Build
+++ b/tools/objtool/Build
@@ -5,9 +5,14 @@
 objtool-y += objtool.o
 
 objtool-y += libstring.o
+objtool-y += str_error_r.o
 
 CFLAGS += -I$(srctree)/tools/lib
 
 $(OUTPUT)libstring.o: ../lib/string.c FORCE
 	$(call rule_mkdir)
 	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)str_error_r.o: ../lib/str_error_r.c FORCE
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)