libproxy: improved to also build/install vala bindings if possible

develop/libproxy/libproxy.conf

@@ -19,3 +19,8 @@ if pkginstalled perl; then
 	# install into 'vendor_perl' directory
 	var_append cmakeopt ' ' "-DPERL_VENDORINSTALL=yes"
 fi
+
+# vala bindings
+if pkginstalled vala; then
+	var_append cmakeopt ' ' "-DWITH_VALA=yes"
+fi