initial commit

This initial commit added the following files
from bpf-next repository:
  src:
    <files from linux:tools/lib/bpf>
    bpf.c bpf.h btf.c btf.h libbpf.c libbpf.h
    libbpf_errno.c netlink.c nlattr.c nlattr.h
    str_error.c str_error.h
  include:
    <files from linux:tools/include/uapi/linux>
    uapi/linux/{bpf.h, btf.h}

    <files from linux:tools/include/tools>
    tools/libc_compat.h

The following files are also added:
  include/linux/{err.h, kernel.h, list.h, overflow.h, types.h}
These files are customized headers to satisfy compilation.
Their original counterparts are at linux:tools/include/linux
directory.

Signed-off-by: Yonghong Song <yhs@fb.com>

include/linux/err.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+#ifndef __LINUX_ERR_H
+#define __LINUX_ERR_H
+
+static inline void * ERR_PTR(long error_)
+{
+        return (void *) error_;
+}
+
+#endif