See https://savannah.gnu.org/patch/index.php?8252. Patch provided
by Anthony G. Basile.
* acinclude.m4 (TAR_HEADERS_ATTR_XATTR_H): Look for <sys/xattr.h>
first and then for <attr/xattr.h>. Link against libattr.so if
needed.
* lib/xattr-at.h: Include sys/xattr.h or attr/xattr.h, depending
on which one is detected.
* src/Makefile.am [TAR_LIB_ATTR] (tar_LDADD): Link against -lattr.
This patch adds *xattr() stubs in case extended attribute support is
not present and implements the *attrat() family of functions. Based
on the patch by Pavel Raiskup <pavel@raiskup.cz> for gnulib.
* acinclude.m4 (TAR_HEADERS_ATTR_XATTR_H): New defun.
* configure.ac: Call TAR_HEADERS_ATTR_XATTR_H
* lib/Makefile.am: Add xattr-at.[ch], distribute attr-xattr.in.h
[!TAR_COND_XATTR_H]: Build attr/xattr.h
* lib/attr-xattr.in.h: New file.
* lib/xattr-at.c: New file.
* lib/xattr-at.h: New file.