Problem reported by Tom G. Christensen in:
http://lists.gnu.org/archive/html/bug-gnulib/2015-04/msg00074.html
* lib/file-has-acl.c: Use GETXATTR_WITH_POSIX_ACLS instead of a
combination of HAVE_SYS_XATTR_H, HAVE_LINUX_XATTR_H, and
HAVE_GETXATTR.
* m4/acl.m4 (gl_FILE_HAS_ACL): Test fot the entire combination of
linux/xattr.h, sys/xattr.h, getxattr, XATTR_NAME_POSIX_ACL_ACCESS,
and XATTR_NAME_POSIX_ACL_DEFAULT, since that's what what
file-has-acl.c actually needs.