protocol: hook up xmllint to check validity
diff --git a/configure.ac b/configure.ac
index 80a5d69..ac3878b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -474,6 +474,17 @@
 	AC_MSG_ERROR([wayland-scanner is needed to compile weston])
 fi
 
+PKG_CHECK_MODULES(WAYLAND_SCANNER, wayland-scanner)
+AC_PATH_PROG(XMLLINT, xmllint)
+AC_ARG_WITH([dtddir],
+	    AS_HELP_STRING([--with-dtddir],
+			   [Directory containing the Wayland
+			    protocol DTD @<:@default=from pkgconfig@:>@]),
+	    [dtddir="$withval"],
+	    [dtddir=$($PKG_CONFIG --variable=pkgdatadir wayland-scanner)])
+AC_SUBST([dtddir])
+AM_CONDITIONAL([HAVE_XMLLINT], [test "x$XMLLINT" != "x" -a "x$dtddir" != "x"])
+
 AC_CONFIG_FILES([Makefile
 		 shared/Makefile
 		 src/Makefile