[PATCH v3 wayland-protocols] configure.ac: Fix compatibility for older pkg-config versions

[Bryce Harrington]

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 at osg.samsung.com>
Cc: Pekka Paalanen <ppaalanen at gmail.com>
Cc: Quentin Glidic <sardemff7+wayland at sardemff7.net>
Cc: Peter Hutterer <peter.hutterer at who-t.net>
---
Changes from v2
   - Place config.m4 into an m4 subdir
   - Auto load m4's via AC_CONFIG_MACRO_DIR

Changes from v1
   - Document why the work around is needed and what obsoletes it.
   - Drop pkgconfigdir, which isn't strictly needed

 configure.ac |  2 ++
 m4/compat.m4 | 12 ++++++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 m4/compat.m4

diff --git a/configure.ac b/configure.ac
index 93688d0..c51b7fc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,6 +11,8 @@ AC_INIT([wayland-protocols],
         [wayland-protocols],
         [http://wayland.freedesktop.org/])
 
+AC_CONFIG_MACRO_DIR([m4])
+
 AC_SUBST([WAYLAND_PROTOCOLS_VERSION], [wayland_protocols_version])
 
 AM_INIT_AUTOMAKE([1.11 foreign no-dist-gzip dist-xz])
diff --git a/m4/compat.m4 b/m4/compat.m4
new file mode 100644
index 0000000..290ef03
--- /dev/null
+++ b/m4/compat.m4
@@ -0,0 +1,12 @@
+dnl noarch_pkgconfigdir only available in pkg-config 0.27 and newer
+dnl http://lists.freedesktop.org/archives/pkg-config/2012-July/000875.html
+dnl Ubuntu 14.04 provides only pkg-config 0.26 so lacks this function.
+dnl
+dnl The Wayland project maintains automated builds for Ubuntu 14.04 in
+dnl a Launchpad PPA.  14.04 is a Long Term Support distro release, which
+dnl will reach EOL April 2019, however the Wayland PPA may stop targeting
+dnl it some time after the next LTS release (April 2016).
+m4_ifndef([PKG_NOARCH_INSTALLDIR], [AC_DEFUN([PKG_NOARCH_INSTALLDIR], [
+    noarch_pkgconfigdir='${datadir}'/pkgconfig
+    AC_SUBST([noarch_pkgconfigdir])
+])])
-- 
1.9.1