Use correct headers/libraries when providing xattr support

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.

acinclude.m4

@@ -37,8 +37,29 @@ AC_DEFUN([TAR_HEADERS_ATTR_XATTR_H],
     [], [with_xattrs=maybe]
   )
 
+  # First check for <sys/xattr.h>
+  AC_CHECK_HEADERS([sys/xattr.h])
+  AM_CONDITIONAL([TAR_COND_XATTR_H],[test "$ac_cv_header_sys_xattr_h" = yes])
+  AM_CONDITIONAL([TAR_LIB_ATTR],[false])
+  if test "$ac_cv_header_sys_xattr_h" = yes; then
+    AC_CHECK_FUNCS(getxattr  fgetxattr  lgetxattr \
+                   setxattr  fsetxattr  lsetxattr \
+                   listxattr flistxattr llistxattr,
+        # only when functions are present
+        AC_DEFINE([HAVE_SYS_XATTR_H], [1],
+                    [define to 1 if we have <sys/xattr.h> header])
+        if test "$with_xattrs" != no; then
+          AC_DEFINE([HAVE_XATTRS],,[Define when we have working linux xattrs.])
+        fi
+    )
+  fi
+
+  # If <sys/xattr.h> is not found, then check for <attr/xattr.h>
+  if test "$ac_cv_header_sys_xattr_h" != yes; then
     AC_CHECK_HEADERS([attr/xattr.h])
     AM_CONDITIONAL([TAR_COND_XATTR_H],[test "$ac_cv_header_attr_xattr_h" = yes])
+    AC_CHECK_LIB([attr],[fgetxattr])
+    AM_CONDITIONAL([TAR_LIB_ATTR],[test "$ac_cv_lib_attr_fgetxattr" = yes])
     if test "$ac_cv_header_attr_xattr_h" = yes; then
       AC_CHECK_FUNCS(getxattr  fgetxattr  lgetxattr \
                      setxattr  fsetxattr  lsetxattr \
@@ -51,4 +72,5 @@ AC_DEFUN([TAR_HEADERS_ATTR_XATTR_H],
           fi
       )
     fi
+  fi
 ])

lib/xattr-at.h

@@ -20,7 +20,15 @@
 #define XATTRS_AT_H
 
 #include <sys/types.h>
+#if defined(HAVE_SYS_XATTR_H)
+# include <sys/xattr.h>
+#elif defined(HAVE_ATTR_XATTR_H)
 # include <attr/xattr.h>
+#endif
+
+#ifndef ENOATTR
+# define ENOATTR ENODATA        /* No such attribute */
+#endif
 
 /* These are the dir-fd-relative variants of the functions without the
    "at" suffix.  For example, setxattrat (AT_FDCWD, path, name, value, size,

src/Makefile.am

@@ -51,3 +51,7 @@ AM_CFLAGS = $(WARN_CFLAGS) $(WERROR_CFLAGS)
 LDADD = ../lib/libtar.a ../gnu/libgnu.a $(LIBINTL) $(LIBICONV)
 
 tar_LDADD = $(LIBS) $(LDADD) $(LIB_CLOCK_GETTIME) $(LIB_EACCESS) $(LIB_SELINUX)
+
+if TAR_LIB_ATTR
+tar_LDADD += -lattr
+endif