configure.ac: Fix compatibility for older pkg-config versions

noarch_pkgconfigdir is not available on oldish pkg-config's.  Among
other things this affects Wayland's nightly auto-build Ubuntu 14.04
PPAs.

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Quentin Glidic <sardemff7+wayland@sardemff7.net>
Cc: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>