tools: Adopt memdup() from tools/perf, moving it to tools/lib/string.c

That will contain more string functions with counterparts, sometimes
verbatim copies, in the kernel.

Acked-by: Wang Nan <wangnan0@huawei.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-rah6g97kn21vfgmlramorz6o@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
new file mode 100644
index 0000000..f3a6db6
--- /dev/null
+++ b/tools/include/linux/string.h
@@ -0,0 +1,9 @@
+#ifndef _TOOLS_LINUX_STRING_H_
+#define _TOOLS_LINUX_STRING_H_
+
+
+#include <linux/types.h>	/* for size_t */
+
+void *memdup(const void *src, size_t len);
+
+#endif /* _LINUX_STRING_H_ */