[gnome-online-accounts] build: Check the existence of pkg-config before using it

[Debarshi Ray <debarshir src gnome org>]

commit 2567d0a004690d99a576c43bf74e7875903a8d88
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Jul 31 14:46:49 2015 +0200

    build: Check the existence of pkg-config before using it
    
    https://bugzilla.gnome.org/show_bug.cgi?id=752270

 configure.ac |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 75418fa..7c36a72 100644
--- a/configure.ac
+++ b/configure.ac
@@ -28,6 +28,8 @@ AC_ISC_POSIX
 AC_HEADER_STDC
 AC_PROG_LIBTOOL
 
+PKG_PROG_PKG_CONFIG(0.16)
+
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
 GOA_MAJOR_VERSION=goa_major_version