configure: check for pkg-config presence

Change-Id: I1484fc8b870df6f0aeef0c13078c66d0cfa97e75
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 4b00af7..e2575c1 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -18,6 +18,13 @@
 AC_PROG_INSTALL
 AC_PROG_RANLIB
 
+dnl check for pkg-config (explained in detail in libosmocore/configure.ac)
+AC_PATH_PROG(PKG_CONFIG_INSTALLED, pkg-config, no)
+if test "x$PKG_CONFIG_INSTALLED" = "xno"; then
+        AC_MSG_WARN([You need to install pkg-config])
+fi
+PKG_PROG_PKG_CONFIG([0.20])
+
 dnl checks for libraries
 AC_SEARCH_LIBS([dlopen], [dl dld], [LIBRARY_DL="$LIBS";LIBS=""])
 AC_SUBST(LIBRARY_DL)